3D Realms has actually released the full source code to Duke Nukem 3D, and you can download it from FileShack. OpenGL, TCP/IP support anyone? The file is a 3.83mb download, and instructions on how to compile it are included. But what about Duke Nukem Forever? Some shocking news here
Newer stuff
Rumor - duke Nukem Forever (not) using Doom 3 engine
http://www.shacknews.com/onearticle.x/33499/
Well looks like they are onto completing the game...when ?
the physics engine
http://www.shacknews.com/onearticle.x/33755/
engine demos
http://www.meqon.com/downloadarea/downloadarea.php
might use xstream
http://www.shacknews.com/onearticle.x/35764/
Found this on the steam forums.
The jeep demo in it is pretty fun. I hope BF 2 will be like that sytle, but better.