FramerD is an object database (ok, a Framestore - but it's something similar) with an integrated DB server, CGI interface, and Scheme scripting language. Ideal for building knowledge databases, as FramerD is optimized for the pointer-heavy structures involved. But also very exciting, as you get a Scheme with server and ODB. I definitely have to play with it, especially since it should also compile on OS X (though it doesn't work for me right now). And it is licensed under GPL. And for the snake charmers among the monkey programmers, there is also an experimental Python library for accessing FramerD...