Lie superalgebras - Irving Kaplansky's material on Lie superalgebras. - http://justpasha.org/math/links/subj/lie/kaplansky/
History of mathematics - Notes by Donald Lancon, Jr. Contains a brief history of calculus and other interesting stuff. - http://www.obkb.com/dcljr/mathemat.html
Why study calculus? - A brief look at some of the history of mathematics by Eric Schechter. - http://www.math.vanderbilt.edu/~schectex/courses/whystudy.html
Graph Theory - Hyperlinked PDF version of a book by Reinhard Diestel. - http://www.math.uni-hamburg.de/home/diestel/books/graph.theory/
Algebra notes - Roy Smith's course notes in linear algebra, elementary abstract algebra, basic graduate algebra, and a survey of the Riemann-Roch theorem from Riemann to Hirzebruch. - http://www.math.uga.edu/%7eroy/
Probability guide for non-mathematicians - Probability theory basics, applications (including to gambling), interpretations, books, free texts. - http://probability.infarom.ro/
Complex Analysis - "A First Course in Complex Analysis" by Matthias Beck, Gerald Marchesi, and Dennis Pixton is a set of lecture notes for a one-semester undergraduate course, relying on as few concepts from real analysis as possible. Numerous exercises are includ - http://math.sfsu.edu/beck/complex.html
Linear Algebra and Applications - Textbook by Thomas Shores. GIFs of pages. - http://www.math.unl.edu/~tshores1/linalgtext.html
The FEMCI Book - Finite Element Modeling Continuous Improvement. A web text by Ryan Simmons. - http://femci.gsfc.nasa.gov/femcibook.html
Voting, Arbitration & Fair Division: Mathematics of Social Choice - An introduction to `social choice theory', which uses mathematics to study the strengths/weaknesses of voting systems, arbitration schemes, and other methods of group decision making. Lots of pictures, requires only basic linear algebra. Author: Marcus Pi - http://xaravve.trentu.ca/pivato/Teaching/voting.pdf
Linear Partial Differential Equations and Fourier Theory - Complete textbook by Marcus Pivato on the solutions of linear partial differential equations, with emphasis on eigenfunction methods (and hence, Fourier analysis). Lots of pictures. - http://xaravve.trentu.ca/pde.pdf
Calculus - Textbook by Gilbert Strang in pdf. - http://ocw.mit.edu/ans7870/textbooks/Strang/strangtext.htm
Measure Theory - A book by D.H. Fremlin. Plain tex sources. - http://www.essex.ac.uk/maths/staff/fremlin/mt.htm
Mathematical Methods of Engineering Analysis - Book by Erhan Çinlar and Robert J. Vanderbei in PDF. Topics covered: functions on metric spaces, differential and integral equations, convex analysis, and measure and integration. - http://www.princeton.edu/~rvdb/506book/book.pdf
Entropy of Compact Group Automorphisms - Lecture notes based on a course at Ohio State in 1994 by Thomas Ward in DVI and PostScript. - http://www.mth.uea.ac.uk/~h720/lecturenotes/
Abstract Algebra Notes - A collection of short notes by Bruce Ikenaga in PostScript. - http://www.millersville.edu/~bikenaga/absalg/absanote.html
Open Math Text Lecture Notes - Lecture notes on various topics (English and Spanish) in Word and PDF format. - http://openmathtext.org/downloads.html
Stochastic Calculus - A fairly complete elementary introduction to the basics of stochastic integration with respect to continuous semimartingales by Alan Bain. All the theory usually needed for basic mathematical finance. Sixty pages in DVI, postscript, and PDF. - http://www.chiark.greenend.org.uk/~alanb/
Hilbert Space Methods for Partial Differential Equations - Textbook for beginning graduate students of mathematics, engineering, and the physical sciences by Ralph Showalter. Chapters in PostScript and PDF. - http://ejde.math.txstate.edu/Monographs/01/abstr.html
Linearization via the Lie Derivative - By Carmen Chicone and Richard Swanson. LaTeX, DVI, PostScript and PDF. - http://ejde.math.txstate.edu/Monographs/02/abstr.html
Finite Fields - An Introduction to Finite Fields by Bill Cherowitzo (html). - http://www-math.cudenver.edu/~wcherowi/courses/finflds.html
Differential Geometry - Lecture notes for an honors course at the University of Adelaide by Michael Murray in HTML with GIFs. - http://internal.maths.adelaide.edu.au/people/mmurray/dg_hons/dg_hons.html
Math Wizard - E-book gives some ideas on alternative approaches to teaching and learning math. Page includes table of contents. Requires a purchase. - http://home.earthlink.net/~susankennison/mathwizard/
Mathematical Logic - "A Problem Course in Mathematical Logic" by Stefan Bilaniuk in LaTeX, PostScript or PDF. - http://euclid.trentu.ca/math/sb/pcml/
Natural Operations in Differential Geometry - By Ivan Kolar, Jan Slovak and Peter W. Michor, originally published by Springer-Verlag in 1993. DVI, PostScript and PDF. - http://www.emis.de/monographs/KSM/
Theory of Symmetry and Ornament - Monograph by Slavik V. Jablan published by the Serbian Academy of Science and Arts in 1995. HTML - http://www.emis.de/monographs/jablan/
Matroid Decomposition - Monograph by Klaus Truemper published by Academic Press in 1992. Chapters in PostScript. - http://www.emis.de/monographs/md/
Spinors, Spectral Geometry, and Riemannian Submersions - Monograph by Peter B. Gilkey, John V. Leahy and Jeonghyeong Park published by Seoul National University in 1998. DVI and PostScript. - http://www.emis.de/monographs/GLP/
Differential Equations - Postscript notes on various topics in differential equations by Bruce Ikenaga. - http://marauder.millersville.edu/~bikenaga/diffeq/deqnote.html
Analytic Differential Equations - Lectures on Analytic Differential Equations by Sergei Yakovenko at the Weizmann Institute. - http://www.wisdom.weizmann.ac.il/~yakov/thebook.pdf
Partial Differential Equations - Lecture notes on Analysis and PDEs by Bruce Driver at UCSD. - http://math.ucsd.edu/~driver/231-02-03/lecture_notes.htm
Ordinary Differential Equations - Course notes by Klaus Schmitt at the University of Utah. - http://www.math.utah.edu/~schmitt/math6410.html
Chaos - Introduction To Chaos by Michael Cross. An online course at Caltech. - http://www.cmp.caltech.edu/~mcc/Chaos_Course/Outline.html
Differential forms - An introduction to differential forms and other notes by Donu Arapura. - http://www.math.purdue.edu/~dvb/
Algorithms and Complexity - By Herbert S. Wilf. In print 1986-1994. Single PDF file. - http://www.cis.upenn.edu/~wilf/AlgComp3.html
Mechanism of the Heavens - A book on celestial mechanics by Mary Somerville (1831). - http://www.malaspina.com/etext/heavens.htm
Functional Analysis - Lecture notes by Paul Garrett. - http://www.math.umn.edu/~garrett/m/fun/
Differentiable manifolds - Lecture notes by Mariusz Wodzicki in postscript or pdf. - http://math.berkeley.edu/~wodzicki/214/
Mathematical Illustrations - A manual of geometry and PostScript by Bill Casselman, including code samples and packages. - http://www.math.ubc.ca/people/faculty/cass/graphics/text/www/
Mathematical Analysis I - This text by Elias Zakon covers the basic topics of undergraduate real analysis including: metric spaces, function limits and continuity, sequences and series of functions, power series, and differentiation and integration. - http://www.trillia.com/zakon-analysisI.html
Meta Math! The Quest for Omega - A mathematical and philosophical book by Gregory Chaitin on logic, information theory, complexity, etc. (available in html or pdf). - http://www.umcs.maine.edu/~chaitin/omega.html
Wavelet Tutorial - Guide to wavelet analysis by Robi Polikar. - http://users.rowan.edu/~polikar/WAVELETS/WTtutorial.html
Number Theory - "An Introduction to the Theory of Numbers" by Leo Moser is a textbook covering following topics: Compositions and Partitions; Arithmetic Functions; Distribution of Primes; Irrational Numbers; Congruences; Diophantine Equations; Combinatorial Num - http://www.trillia.com/moser-number.html
Description Logics Handbook - A course on Description Logics (the Semantic Web underlying formalism) by E. Franconi (modules in pdf) - http://www.inf.unibz.it/~franconi/dl/course/
Sheaf Cohomology - Mathematical notes on sheaves and other topics by P. Morandi. - http://sierra.nmsu.edu/morandi/notes/mathematicalnotes.html
Geometry and the Imagination - An online course by John Conway, Peter Doyle, Jane Gilman and Bill Thurston in HTML and PostScript. - http://www.geom.uiuc.edu/docs/education/institute91/
Flatland - A romance of many dimensions. With Illustrations by the Author, A SQUARE (Edwin A. Abbott 1838-1926). HTML. - http://www.geom.uiuc.edu/~banchoff/Flatland/
Calculus Using Infinitesimals - Elementary Calculus: An Approach - a book by H. Jerome Keisler originally published by Prindle, Weber & Schmidt (2nd ed: 1986) - http://www.math.wisc.edu/~keisler/calc.html
Abstract Algebra - A book draft: "Applied Abstract Algebra" by D. Joyner, R. Kreminski, J. Turisco in HTML. - http://web.usna.navy.mil/~wdj/book/
Abstract Algebra with GAP - A laboratory manual by J. G. Rainbolt and J. A. Gallian. - http://euler.slu.edu/Dept/Faculty/rainbolt/manual.html
Topology Without Tears - A course in topology by Sidney A. Morris in HTML with embedded GIFs. Must purchase to view. - http://www.theassayer.org/cgi-bin/asauthor.cgi?author=430
Harmonic Analysis and Partial Differential Equations - A book by Dahlberg and Kenig in postscript (bitmapped fonts). The page also contains another book by Dahlberg: "Icke Linjära Evolutionsekvationer" (Swedish). - http://www.math.chalmers.se/Math/Research/GeometryAnalysis/Lecturenotes/
Riemannian Geometry - "An Introduction to Riemannian Geometry" by S. Gudmundsson in postscript (1996). - http://www.maths.lth.se/publications/Pure-Lecture-Notes.html
Splines and Wavelets - A monograph by Karl Scherer in German (DVI and Postscript). - http://www.iam.uni-bonn.de/~scherer/wavelets.html
Complex Numbers - Dave's Short Course on Complex Numbers (David Joyce). - http://www.clarku.edu/~djoyce/complex/
Dynamics and Chaos - Class notes by Evans M. Harrell II for an introductory course on dynamical systems and chaos, taken by mathematicians, engineers, and physicists. This text concentrates on models rather than proofs in order to bring out the concepts of dynamics and chaos - http://www.mathphysics.com/dynam/
Multigrid Methods - "An Introduction to Multigrid Methods" by Pieter Wesseling. - http://www.mgnet.org/mgnet-books-wesseling.html
Optimization - "Lecture Notes on Optimization" by Pravin Varaiya. This book is an introduction to mathematical programming, optimal control, and dynamic programming. - http://www-path.eecs.berkeley.edu/~varaiya/papers_ps.dir/NOO.pdf
Toposes, Triples and Theories - A book by Michael Barr and Charles Wells originally published by Springer Verlag. - http://www.cwru.edu/artsci/math/wells/pub/ttt.html
Algebraic Geometry - Various lecture notes by J.S. Milne. - http://www.jmilne.org/math/
Wavelets - An Introduction to Wavelets by Amara Graps in HTML, PDF or Postscript. - http://www.amara.com/IEEEwave/IEEEwavelet.html
Numerical Grid Generation - A book by Thompson, Warsi, and Mastin, previously published by Elsevier, in HTML. - http://www.erc.msstate.edu/publications/gridbook/
Linear Algebra - "Elementary Linear Algebra" by Keith Matthews. Lecture notes and solutions from 1991 in PDF or PostScript. - http://www.numbertheory.org/book/
Matrices - The 1934 classic "Lectures on Matrices" by Wedderburn in scanned PDF. - http://www.ams.org/online_bks/coll17/
Finite Simple Groups - "The classification of the finite simple groups" by D. Gorenstein, R. Lyons, and R. Solomon in PDF. - http://www.ams.org/online_bks/surv40-1/
Homeomorphisms in Analysis - A survey by C. Goffman, T. Nishiura, D. Waterman in PDF. In particular, the effects of homeomorphic changes of domain on the analyticity of a function are studied. - http://www.ams.org/online_bks/surv54/
Differential Algebra - Scans of Ritt's 1950 classic in PDF. - http://www.ams.org/online_bks/coll33/
Geometric Asymptotics - This book by Guillemin and Sternberg includes the method of stationary phase, geometrical optics, quantization. - http://www.ams.org/online_bks/surv14/
Numerics - interactive - In this PDF book by Thomas Risse, basic numerical algorithms are presented and implemented in order to determine the precision of computation, to solve systems of linear equations, to evaluate elementary functions, to find zeros, to integrate and to solve - http://www.weblearn.hs-bremen.de/risse/MAI/docs/numerics.pdf
Basic Concepts of Mathematics - This text by Elias Zakon helps the student complete the transition from purely manipulative to rigorous mathematics. Chapters cover Set Theory, the Real Numbers, and n-dimensional Geometry. - http://www.trillia.com/zakon1.html
Differential Geometry and General Relativity - An introduction to differential geometry and general relativity by Stefan Waner at Hofstra. This is an upper level undergraduate mathematics course which assumes a knowledge of calculus and some linear algebra. - http://people.hofstra.edu/faculty/Stefan_Waner/diff_geom/tc.html
Plane Geometry - Shalosh B. Ekhad XIV. A fully illustrated and completely self-contained Elementary Geometry textbook (ca. 2050), downloaded from the future by Doron Zeilberger. Entirely written in Maple. - http://www.math.rutgers.edu/~zeilberg/GT.html
The Limits of Mathematics - An online course on information theory and the limits of formal reasoning by G.J. Chaitin. - http://www.umcs.maine.edu/~chaitin/lm.html
Geometric Constraint Solving - An electronic primer by William Bouma, Xiangping Chen, Ioannis Fudos, Christoph Hoffmann, and Pamela J. Vermeer. - http://www.cs.purdue.edu/homes/cmh/electrobook/intro.html
Differential Topology - Course notes by Matthew G. Brin in PostScript including "Introduction to Differential Topology", "Introduction to Seifert fibered 3-manifolds", "Groups acting on 1-dimensional spaces", and "Presentations, conjugacy, roo - http://www.math.binghamton.edu/matt/
Travelling Wave Solutions of Parabolic Systems - Translation of a monograph by Aizik Volpert, Vitaly Volpert, and Vladimir Volpert published by AMS in 1994. Whole book or chapters in PDF. - http://www.ams.org/online_bks/mmono140/
Algebraic Topology - 1942 classic by Solomon Lefschetz published by AMS. Chapters in scanned PDF. - http://www.ams.org/online_bks/coll27/
Several complex variables - Several sets of lecture notes by Jean-Pierre Demailly, some in French, including "Potential theory in several complex variables", and "Multiplier ideal sheaves and analytic methods in algebraic geometry" in DVI or PostScript. - http://www-fourier.ujf-grenoble.fr/~demailly/lectures.html
Complex Dynamics in Higher Dimensions - CBMS lecture notes by John Erik Fornæss at the bottom of page with other papers by the author and Nessim Sibony. PostScript. - http://www.math.lsa.umich.edu/~fornaess/complexdynamicspapers.html
Global Analysis - "The Convenient Setting of Global Analysis" - foundations of differential calculus in infinite dimensions with applications to differential geometry and global analysis by Andreas Kriegl and Peter W. Michor published by AMS in 1997. Whole book - http://www.ams.org/online_bks/surv53/
Functional Analysis and Semi-Groups - Book by Einar Hille and Ralph S. Phillips published by AMS in 1957. Scanned chapters in PDF. - http://www.ams.org/online_bks/coll31/
Dynamical Systems - 1927 classic by George D. Birkhoff published by AMS. Scanned chapters in PDF. - http://www.ams.org/online_bks/coll9/
Multiplier Ideals for Algebraic Geometers - Draft of a part of a book in preparation on positivity in algebraic geometry by Robert Lazarsfeld. DVI and PostScript. - http://www.math.lsa.umich.edu/~rlaz/
Category Theory - "A Gentle Introduction to Category Theory - the calculational approach" by Maarten M. Fokkinga in PostScript. - http://wwwhome.cs.utwente.nl/~fokkinga/mmf92b.html
Complex and Functional Analysis - Lecture notes by Douglas N. Arnold for a course at Penn State. Two parts in TeX, DVI, PostScript and PDF. - http://www.math.psu.edu/dna/502.s97/
Advanced Calculus and Analysis - Lecture notes by Ian Craw from a course at the Univ. of Aberdeen. HTML with GIFs. - http://www.maths.abdn.ac.uk/~igc/tch/ma2001/notes/notes.html
Analysis WebNotes - Online course by John Lindsay Orr. Chapters also available in LaTeX. - http://www.math.unl.edu/~webnotes/home/home.htm
Trigonometry - "Dave's Short Trig Course" by D. E. Joyce. HTML with Java. - http://aleph0.clarku.edu/~djoyce/java/trig/
Topology Course Lecture Notes - By Aisling McCluskey and Brian McMaster. HTML with symbol fonts, DVI and PostScript. - http://at.yorku.ca/i/a/a/b/23.htm
Multivariable Calculus - Textbook by George Cain and James Herod. Chapters in PDF. - http://www.math.gatech.edu/~cain/notes/calculus.html
Abstract Algebra II - A companion volume to "Abstract Algebra" by John A. Beachy and Bill Blair published by Waveland Press in 1995. Chapters in PostScript. - http://www.math.niu.edu/~beachy/abstract_algebraII/
Semi-Simple Lie Algebras and their Representations - Book for particle physicists by Robert N. Cahn. Published by Benjamin-Cummings in 1984. Chapters in PostScript. - http://www-physics.lbl.gov/~rncahn/book.html
Templates for the Solution of Linear Systems - Book on iterative methods by Richard Barrett et al. in HTML and Postscript. - http://netlib2.cs.utk.edu/linalg/html_templates/Templates.html
C*-Algebras - "An Introduction to C*-Algebras" by Pierre de la Harpe and Vaughan Jones. The site is in French, but the book is in English. Chapters in PostScript. - http://www.unige.ch/math/biblio/preprint/cstar/liste.html
Universal Algebra - "A Course in Universal Algebra" by Stanley Burris and H. P. Sankappanavar. PostScript and PDF. - http://www.thoralf.uwaterloo.ca/htdocs/ualg.html
Elements of Abstract and Linear Algebra - Foundational textbook on abstract algebra with emphasis on linear algebra by Edwin H. Connell. Whole book or chapters in DVI, PostScript, and PDF. - http://www.math.miami.edu/~ec/book/
Practical Foundations of Mathematics - An account of the foundations of mathematics (algebra) and theoretical computer science, from a modern constructive viewpoint by Paul Taylor. Published by Cambridge University Press. HTML approximation. - http://www.dcs.qmw.ac.uk/~pt/Practical_Foundations/html/summary.html
Tensor Calculus and Continuum Mechanics - Textbook by John H. Heinbockel. Whole book or chapters in PostScript and PDF. - http://www.math.odu.edu/~jhh/counter2.html
Numerical Recipes Books On-Line - The complete Numerical Recipes books in C, Fortran 77, and Fortran 90 On-Line, in both PostScript and Adobe Acrobat formats. - http://www.nr.com/nronline_switcher.html
A=B - Combinatorics text by Marko Petkovsek, Herbert Wilf and Doron Zeilberger. Published by A. K. Peters. PDF. - http://www.cis.upenn.edu/~wilf/AeqB.html
Probability - "Introduction to Probability" by Charles M. Grinstead and J. Laurie Snell in PDF. Published by the AMS. The site also contains additional teaching resources. - http://www.dartmouth.edu/~chance/teaching_aids/books_articles/probability_book/book.html
Fundamentals of Model Theory - Introductory textbook by William Weiss and Cherie D'Mello. PostScript, DVI, GIF. - http://at.yorku.ca/i/a/a/i/10.htm
Euclid's Elements - Edited by D.E. Joyce. HTML text with Java applets. - http://aleph0.clarku.edu/~djoyce/java/elements/toc.html
Generatingfunctionology - By Herbert S. Wilf. Published by Academic Press. PDF. - http://www.math.upenn.edu/~wilf/DownldGF.html
Linear Methods of Applied Mathematics - Textbook suitable for a first course on partial differential equations, Fourier series and special functions, and integral equations by Evans M. Harrell II and James V. Herod. HTML, RTF and PDF with Maple and Mathematica worksheets. - http://www.mathphysics.com/pde/