Since I always was fan of the DEVIL editor, I took a bit efford in porting it to SDL and making it usable on modern operating systems.
For the case that I am not the last Devil fan, I created a Sourceforge project for it: http://sdldevil.sourceforge.net/
Here you can get the sourcecode and win32 binaries of the version 0.2, the first public release.
Please keep in mind that this is in Alpha state, some features are still not working. But my alphatest showed that it's pretty stable and possible to create levels with it
Also posted on DXX-Rebirth and Descent TaskForce forums by developer.