Very cool: Loom Knowledge Representation System is open sourced
ISI has spent years developing LOOM (written in Common LISP) and the newer PowerLoom (runtime available in Java, Lisp, C++) as knowledge representation tools. Good stuff!
For non-commercial (research) applications, the Java runtime of PowerLoom is probably the way to go. However, PowerLoom is (I think) very expensive for commercial applications.
I use LispWorks, and I have been using LOOM for research, so it is good to know that if I need to, it can be freely used (read the license) for any type of application.