DMSP is a quake mod that lets you play an SP game in any DM map. DMSP for Q4 was originally an internal experiment to see if a new gametype was possible entirely within script. The basic premise is to provide the player an arcade-style limitless supply of monsters and pickups. A deathmatch map is the perfect place for it, because it has a closed connected layout the player can run around in as long as he can stay alive, henceforth the term "deathmatch single player." Q4DM4 was determined to be the best map for the job, because almost the entire layout is navigable without the use of jump pads or teleporters (which the AI doesn't pay attention to). Maps like Q4DM5 had too many isolated platforms that would fill up with monsters that couldn't go anywhere. The experiment was a success aside from a few small issues.
This comment is currently awaiting admin approval, join now to view.