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.
This is the 0.74 release. Load in Zandronum or ZDoom/GZDoom with a levelset of your choice, and go wild!
looks awesome!