Source is a 3D video game engine developed by Valve Corporation. It debuted in June 2004 with Counter-Strike: Source, followed shortly by Half-Life 2, and has been in active development ever since. Source does not have a meaningful version numbering scheme; instead, it is designed in constant incremental updates. Source was created to power first-person shooters, but has also been used professionally to create role-playing, side-scroller, MOBA, puzzle, MMORPG, top-down shooter and real-time strategy games.