Modifications
Like its predecessors, Quake 4 can be heavily modified. This led to Quake 4 versions of popular mods from previous versions of Quake, such as Rocket Arena, and Quake 4 Fortress (the Quake 4 version of Team Fortress). Q4F was abandoned before its creators considered it complete; instead they released an alpha version complete with source code.
In the competitive gaming scene, there were two principal mods, Q4Max and X-Battle. The online Quake 4 competitive community was split between the two mods. A number of the online leagues switched between X-Battle and Q4Max, such as ClanBase EuroCup and GGL. Despite this split in the online community, the offline professional LAN tournaments run by CPL, ESWC, WCG, QuakeCon, and WSVG all used Q4Max.
Members of both the Q4Max and X-Battle teams joined forces with Adam 'SyncError' Pyle of id Software and developed another mod, Delta CTF, which brought Quake II style CTF to Quake 4.
Another notable mod is SABot, which successfully implemented multiplayer bots in Quake 4 less than a month after the SDK was released, despite this being a feature that some reviewers criticised Quake 4 for not including.
Read more about this topic: Quake 4