Ever since id Software released their game source code for the original Doom back in 1995 there has been an explosion of third party modifications for a ton of games, from Doom to Quake to Unreal to Half-Life to Tribes to Battlefield 1942 to current games like Half-Life 2, Battlefield 2 and Unreal Tournament 2004.

There is no question that developers who have offered up source code and editing tools for games have done three big things for the PC game industry. First they have extended the life of a number of PC titles far beyond the normal retail time span. They have also served as excellent stepping stones for programmers, level designers, artist and more to learn their craft and to be able to join the game industry as professions. Finally the designs for a number of third party mods have matched and even exceeded professionally released titles.