an Open Source Probabilistic Information Retrieval library, a highly adaptable toolkit to allow developers to easily add advanced indexing and search facilities to their own applications.
a source code tag system that works the same way across diverse environments. You can locate a specified object in the source files and move there easily. It is useful for hacking a large project containing many subdirectories, many #ifdef and many main()
a language system for specifying concurrent, hierarchical, finite state machines (an implementation of "statecharts") to model and control reactive systems.
a pure Java implementation of the Ruby interpreter is tightly integrated with Java to allow both to script any Java class and to embed the interpreter into any Java application.
a collection of machine learning algorithms for data mining tasks. The algorithms can either be applied directly to a dataset or called from your own Java code.