Commons Logging
The Logging package is an ultra-thin bridge between different logging libraries. Commons components may use the Logging API to remove compile-time and run-time dependencies on any particular logging package, and contributors may write Log implementations for the library of their choice.

Gflog
qflog is a tool for displaying log messages which is built on top of the de.qfs.lib.log package of our Java library qflib. It can be used to conveniently browse log messages, searching for those that may be of relevance to some problem. Messages can be sorted, various kinds of filters can be applied and there is support for incremental search and bookmarks.

Houston
Houston is an open-source, light-weight status and logging toolkit offering a plug-in architecture to let you choose the underlying, industry-strength logging toolkit such as Apache log4j or Java 1.4's built-in java.util.logging toolkit. Houston uses the publish/subscribe model and sends reported errors, warnings, infos, hints, and so on to subscribed status handlers.

jLo
jLo is a logging framework written in Java. It has some uniqiue features compared to other existing frameworks.

JTraceDump
JTraceDump provides a facility to keep a history of application processing steps in memory and dump it in case of an error. It is not a replacement, but an addition to trace- or debug-logging.

Just4Log
Just4Log is a library to enhance dynamically the performance of various logging systems inside a java application. Dynamically because the sourcecode in java is not modified but rather the optimization occurs on the compiled ByteCode files.

LN2
LN2 is a logging framework based on pattern matching for the logging process. It's designed loosely on Log4J, without binding categories to levels quite so tightly.

Log4Ant
Collection of Ant tasks that let a build script issue custom messages and diagnostics to remote monitors (like Chainsaw) via Apache's Log4J framework.

Log4j
With log4j it is possible to enable logging at runtime without modifying the application binary. The log4j package is designed so that these statements can remain in shipped code without incurring a heavy performance cost. Logging behavior can be controlled by editing a configuration file, without touching the application binary.

Lumberjack
The Lumberjack project provides an open source (covered by the GNU Lesser Public License) implementation of the logging APIs first introduced in JDK 1.4 that will work for JDK 1.2 and 1.3. The goal is for this implementation to work transparently on JDK 1.2 and 1.3 without recompile and with no significant difference in behavior between it and the implementation provided in JDK 1.4.