QuakeWorld, without loosing any (backwards) compatability.
All QuakeWorld clients should be able to connect to an FTE server, and all FTE
clients should connect to any other QW server.
The FTE client, supports Quake, NetQuake, QuakeWorld, Quake II, Quake III
Arena, Hexen 2, Nexuiz and others.
WWW: http://fteqw.com/