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.
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.