The doomsday engine [opengl]: http://www.doomsdayhq.com/ extra files for doomsday [textures, models, gui, etc]: http://files.dengine.net/index.php Risen3d [d3d,opengl]: http://www.risen3d.newdoom.com/ extra files for risen3d [textures, models, gui, etc]: http://www.risen3d.newdoom.com/downloads.htm Zdaemon, multiplayer doom [software, d3d]: http://zdaemon.org/ Skulltag, custumised multiplayer doom [opengl, software]: http://www.skulltag.com zdoom, enhanced engine [software]: http://www.zdoom.org gzdoom, enhanced engine [opengl]: http://www.grafzahl.drdteam.org