Doom Legacy is a source port of Doom available for various operating systems
which was originally written as a fork of DOSDoom introducing lots of useful
improvements yet retaining original feel of the game.  It currently features:

  * TCP/IP multiplayer networking (including a master server for Internet
    game searches)
  * Nearly complete Boom and Heretic support
  * OpenGL rendering
  * Higher resolutions
  * Console with support for key bindings (Quake-style)
  * FraggleScript for scripting
  * 3D floors, water, and coloured lighting
  * Mouse aim and crosshairs
  * Jumping
  * 32 players (including support for custom skins)

WWW: http://doomlegacy.sourceforge.net/