CsDoom

csDoom is a source port, originally based on ZDoom version 1.22, that was created in 2000 by Sergey Makovkin (Fly). He intended to replace ZDoom's peer-to-peer multiplayer code with a client/server system using code from QuakeWorld. Makovkin achieved his goal, and by December 2000, csDoom already had a decently stable and well-functioning client/server multiplayer mode.

The early versions of csDoom received criticism, particularly from Tom Robinson (Mystican), for being distributed only in binary form. Fly soon relented and released the source code, but in July 2000, examination of the code revealed that a hard-coded ban of Robinson's IP address was in place. Additionally, a backdoor was present that would give a player remote console access to any server if their nickname was "Fly", "fly" or "FLY".

In January 2001, Makovkin announced that he no longer had enough time to work on csDoom. While the project remained on hiatus, a new port based on csDoom, ZDaemon, surfaced, and Skulltag began using csDoom's networking code. Later, csDoom development was taken over by Denis Lukianov in 2004. The last version of csDoom was 1.3, released in January 28, 2006. Active development has moved on to project Odamex, which is the unofficial successor to csDoom.