Logging with log4j - An Efficient Way to Log Java Applications
- About the need for logging and Log4j, an Open Source framework for logging Java applications for debugging and monitoring purposes.
- http://www.developer.com/open/article.php/3097221

Java Logging Framework
- Framework for logging in Java. [Open source]
- http://www.theobjectguy.com/javalog/

Log4j
- Logging package for printing log output to different local and remote destinations. Selection and filtering of log events at runtime. [Open Source, APL]
- http://logging.apache.org/log4j/docs/

JDBCAppender
- Log4J compatible for logging messages to database. [Open Source, APL]
- http://www.dankomannhaupt.de/projects/

Log4E
- A Eclipse plugin which helps use logger easily in Java Projects. It's not bound to any special logging framework, but can used with Log4j, Commons Logging, or custom logger.
- http://log4e.jayefem.de/

Jestr - a Java Extensible Stringifier
- Converts arbitrary Java objects into strings for logging. Configured via a properties file similar to log4j.properties. [Open Source, APL]
- http://jestr.sourceforge.net/

Java Logging API Specification
- The home of a Java Community Process expert group defining standard logging APIs for error and trace logging. The latest draft and status history is available.
- http://jcp.org/en/jsr/detail?id=047

Chainsaw
- An application for visual viewing and filtering of log4j events. [Open Source, GPL]
- http://logui.sourceforge.net/

jLEA (Journaling and Logging Enterprise Applications)
- A logging system written in pure Java for logging and supervising non-distributed as well as distributed Java-, J2EE- and legacy applications. [Commercial]
- http://www.jlea.de/

Lumberjack
- This API Conforms to the Logging API in JDK1.4, but is available for pre-1.4 JDKs.
- http://javalogging.sourceforge.net/

IBM Logging Toolkit for Java
- Provides logging, tracing functions, and filters. Part of the IBM alphaWorks project. [Commercial]
- http://www.alphaworks.ibm.com/aw.nsf/techmain/loggingtoolkit4j

Java Syslog
- Java based syslogd client and server implementation. [Open Source, GPL]
- http://www.trustice.com/java/syslog/

JavaLog
- A logging class library with runtime configurable formatting and event filtering. [Open Source, MPL]
- http://sourceforge.net/projects/javalog/

JLogger
- An implementation of the Java logging API (java.util.logging) including a graphical user interface. [Open Source]
- http://www.javelinsoft.com/jlogger/

Quality Open Software (QOS)
- Offers support on log4j as well as information concerning a book on this topic.
- http://qos.ch/