This addon works with all maps made for ZDaemon's version of this mode, it additionally works with most mods. Unless that mod changes the player's TID, if that's the case it sadly won't work. But you should try the mods you are going to play with it before giving up.
It also comes with a standalone railgun, which is required if the maps you are going to play use ZDaemon's or Skulltag's railgun. If you are loading Skulltag Content too, this is not necessary. The filename for it is "ZDoom_KOTH_Railgun.pk3"
Fully compatible with both Zandronum and ZDoom. Remember to activate Team Deathmatch (and NOT Teamgame) and set your fraglimit to 0.
Spoiler: Screenshot (Open)DOWNLOAD!
For convenience, here's a link to some KOTH maps: