FastGEO Computational Geometry Library - FastGEO, A computational geometry library written in the object pascal language. - http://www.partow.net/projects/fastgeo/index.html
Qhull - Computes convex hulls, Delaunay triangulations, Voronoi diagrams, half-space intersections about a point, furthest-site Delaunay triangulations, and furthest-site Voronoi diagrams. It runs in 2-d, 3-d, 4-d, and higher dimensions. - http://www.qhull.org/
Mg R-tree Library - A simple C++ R-tree implementation with Segment Incidences Detector as an application. - http://www.volny.cz/r-tree/
CGAL - Computational Geometry Algorithms Library - A collaborative effort to develop a robust, easy to use, and efficient C++ software library of geometric data structures and algorithms. - http://www.cgal.org/
Polymake - A tool for the algorithmic treatment of polytopes and polyhedra. - http://www.math.tu-berlin.de/polymake/
Smallest Enclosing Ball of Points - Fast and robust C++ code available under GNU license. Handles arbitrary dimensions, and has high numerical stability. - http://www.inf.ethz.ch/personal/gaertner/miniball.html
Knotenpunkt - Produces commercial software that creates a surface model out of a pointcloud or polymesh [Balingen, Germany]. - http://www.knotenpunkt.com/home_E.htm
CM2 Mesh Tools - Professional C++ mesh generators. Includes product information and news releases. - http://www.computing-objects.com/en/meshtools.html
Triangle - Jonathan Richard Shewchuk's Two-Dimensional Quality Mesh Generator and Delaunay Triangulator. - http://www.cs.cmu.edu/~quake/triangle.html
Surface Evolver - Free interactive program for modelling liquid surfaces shaped by various forces and constraints, e.g., minimal surfaces (bubbles). Applies gradient descent to minimize energy. Available for most platforms. - http://www.susqu.edu/facstaff/b/brakke/evolver/
Knotplot - A program for exploring topological knots and knot-like objects in a 3-D rendered environment offering stills, animated knots (including dynamic forces) and demos. Aimed at mathematician and artist alike. - http://www.cs.ubc.ca/nest/imager/contributions/scharein/KnotPlot.html
Edgebreaker 3D Compression for Triangle Meshes - Source code, explanations, file formats, and examples of the Edgebreaker compression and decompression techniques. - http://www.gvu.gatech.edu/~jarek/edgebreaker/eb/
GTS - The GNU Triangulated Surface Library - Open-source library for manipulating 3D triangular surface meshes. Delaunay triangulations, robust geometric predicates, robust boolean set operations on surfaces, surface refinement and coarsening, level-of-detail, k-d trees, volume and curvature, strip - http://gts.sourceforge.net/
Gmsh - Gmsh is a three-dimensional finite element mesh generator, primarily Delaunay, with built-in pre- and post-processing facilities. Gmsh is freely available for Windows and most UNIX platforms. - http://www.geuz.org/gmsh/
JeoEdit - Two Java applets for editing polygons and point sets for input to computational geometry software. - http://cgm.cs.mcgill.ca/~godfried/jeoedit/
Delaunay Triangulation Code - J-D. Boissonnat et al.'s code for Delaunay meshing in 2 and 3 dimensions in C++. - http://www-sop.inria.fr/prisme/logiciel/del-tree.html
QMG project - Mesh generation in 2D and 3D on Unix and NT, and related software by Steven Vavasis. - http://www.cs.cornell.edu/Info/People/vavasis/qmg-home.html
Fast Industrial-Strength Triangulation - By Martin Held. Copes with polygons with holes and degeneracies/self-intersections; based on repeatedly clipping ears. Source code on request. - http://www.cosy.sbg.ac.at/~held/projects/triang/triang.html
Computational Geometry Code - Jeff Erickson's links to freely available implementations of geometric algorithms and software. - http://compgeom.cs.uiuc.edu/~jeffe/compgeom/code.html