Zandronum is a free open-source advanced multiplayer sourceport capable of running various games such as Doom, Doom II, Final Doom, Heretic, Hexen, and as well as others online. It originated from Skulltag, which was based on ZDoom and its counterpart, GZDoom.
Yes, this crap is finally released. Now it can get off my back. All the notes you need are in the RAR archive comments BUGS: may not work with zandronum/skulltag because of a custom actor cast