Get ready for the craziest DooM mod you've ever seen - DooD! And also DooD 2 in this release. It reverses EVERYTHING by a half (ok, almost things) - pictures, sounds, music and even maps! You can use everything as one pack (use .bat files included in archive) or some wads separately.
Daimonas (gfx, sounds)
DarkNem (gfx, messages)
DeXiaZ (maps, music, ending messages, map names)
Kaiser (PSX Doom maps for episode 5 and map34-35)
SolidJenner (Revenge of the Prinnies addon)
IWADs: DooM for DooD; DooM 2 for DooD 2
Sourceport: anything zdoom-family related (zdoom, gzdoom, zandronum).
Revenge of the Prinnies addon: