Platform-independent C-API library implementing the Record-JAR file format, with mappings to other languages/technologies, including C++, COM, D, .NET, Python, Ruby, and STL.
Fastjar is an implementation of Sun's jar utility that comes with the JDK, written entirely in C, and runs in a fraction of the time while being 100% feature compatible.
Tool for automatic generation of UML Class Diagrams out of Java Class Files. Originally designed as a command line tool to convert .class/.jar files into .emf/.eps files, it now offers a visual environment.