Apache logging services
The Apache Logging Services Project creates and maintains open-source software related to the logging of application behavior and released at no charge to the public.
Apache Log4j 2
Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j 1.x.
A versatile logging framework for PHP. Originally a port of Apache log4j to PHP, it has grown to include various PHP specific features.
A port of the excellent Apache log4j framework to the Microsoft .NET runtime.
A GUI based log viewer. Chainsaw is a companion application to log4j written by members of the log4j development community.
The original Apache logging framework for Java.
Apache log4cxx is a logging framework for C++ patterned after log4j.
Apache log4j extras
Extras for log4j 1.x, like companions, receivers and more.