Want to make your own Hold The Flag map? Download the prefab by clicking here.
htf_doom2 is a simple gamemode conversion of Zombie Survival Doom II which uses my own Hold The Flag prefab. This project didn't require much effort from my part so it was well worth pursuing. I am uncertain whether this map will be fun to play outside of ZS, but only playtesting can tell.
Hold The Flag explanation
There is a neutral flag in the middle of the map that activates 30 seconds into a game, and each team has the goal of having possession of the flag for a total of 2 minutes between their players. As soon as the flag is dropped, it becomes neutral again, though it cannot be picked up by the dropping team for a few seconds. After 10 seconds of not being touched, the flag returns to its original position. Spawns are mostly randomised to prevent flag-camping.
As far as server requirements go, there aren't really any. You're free to tell me of one if you happen to find it.