Jorrit writes: "AresEd is a Free and Open Source 3D Game Creation Kit based on Crystal Space. It currently runs on GNU/Linux and Windows. It is alpha software right now but when it is ready you will be able to create full 3D games using this tool. You can download a few binaries and the source here: http://code.google.com/p/ares/
I'm also looking for developers who are interested in helping me develop this project. Please contact me if you are interested."