JStack Analyzer analyzes jstack output and provides valuable insight for troubleshooting JVM problems.
Sample Profiler is a java agent that provides jstack functionality in addition to method and thread statistical information, all accessible via the JConsole MBean interface.
Modifly is an obfuscator that can do run-time transformations (Patent Pending). What does this mean? Never run the same application byte code again!
Feenix is a class-reloading tool similar to JRebel. It is based on the Instrumentation API, which has some major limitations. Stayed tuned for a new version of Feenix, which is much closer to JRebel.
Heapster is a java agent which monitors garbage collection of objects. Using the Heapster client, you can see graphs of object allocation, the stack traces for object allocation, object histograms, explore retained heap, and much more. This can all be done without using jmap. Just connect the Heapster client to your host JVM! Warning! The object graph functionality is not practical for most JVMs and is somewhat a failed experiment.
Thorax is a bytecode debugger, which allows you to pause program execution, examine and modify variables without the availability of any source code. Thorax is a handy tool to help you understand third party libraries.