It's a new BSP editor written by SleepWalkR that you can grab here: Kristianduske.com
There's plenty of documentation and it's a very easy UI to get into.
Version 1 was used, but version 2 is well into development and promising lots of interesting features.
All in all, a very powerful editor thats definitely worth a look if you've got an interest in creating levels for FPS games.
