<a href="http://zdaemon.org/">ZDaemon</a> is a fun client/server version of Doom with experience points and a large community. <a href="http://forums.zdaemon.org/viewtopic.php?t=2900">GZLauncher</a> is a GTK2+ ZDaemon launcher/game browser, which is pretty much required to play the game. Reproducible: Always Steps to Reproduce: 1. 2. 3.
As mentioned on its homepage, there is currently only a server available for Linux. A client is unlikely in the near future, due to lack of developer motivation, with the recommendation being to run the client in Wine: http://forums.zdaemon.org/viewtopic.php?t=6584 http://forums.zdaemon.org/viewtopic.php?t=6839 http://forums.zdaemon.org/viewtopic.php?t=6908
Feel free to REOPEN this if there's ever a Linux version.