Log5j is a lightweight and fast java logging library for Java versions 5 and above. It is very similar to log4j in style, but uses Java 5's varargs feature to allow any number of arguments to be passed to any logging method.
At an early stage of development. Application/middleware usage monitoring/reporting. Focus on business transactions/use cases to help communicate with users. Small footprint, easy to use GUI and a level of statistical analysis to summarise the data.
Stat4j is a simple lightweight extension to the popular Java logging package log4. It allows logs to be intercepted and mined in real-time for application statistics including performance metrics.