This user-made level for "Duke Nukem: Manhattan Project" features a canyon-style environment with "GLOPP falls".
The map files have been put into a zipfile which you simply have to extract into your DNMP directory. In order to start the map, open the console (^) and type map ccf.
This is an updated version of the map initially made in 2003, with some fixes that should eliminate potential crashes.

A full custom-made episode with 11 levels for "Duke Nukem: Manhattan Project" in which Duke explores a futuristic Washington DC.
The maps have been put into a zipfile. Decompress the "duke" folder to your DNMP directory. In order to start the episode, open the console (^) and type map dukemissiondc_01.
Note that you can only quicksave. If you quit the game before completing the episode, your progress will be lost! In this case, you can load any episode level manually by typing map dukemissiondc_## (with "##" being level number 01-11) in the console.

Finally there's an OpenGL port for the old Apogee classic "Rise of the Triad", and even in its early stages it's looking good already!
This compilation contains the executable as well as the DLL and graphics packs (featuring some highres textures and models, e.g. for the stone columns or rising platforms). You will still need 4 files from your ROTT CD: "Darkwar.wad", "Darkwar.rtl", "Darkwar.rtc" and "remote1.rts".
Since I cannot provide any support for this, you should check Birger's site for further questions and a contact email address (also see zipfile readme).