Source is a
3D video game engine developed by
Valve Corporation as the successor of
GoldSrc. It debuted with in June 2004, followed shortly by
Half-Life 2, and has been in active development since. Source does not have a concise
version numbering scheme; instead, it is designed in constant incremental updates. The successor, Source 2, was officially announced in March 2015. The first game to use it was
Dota 2, being ported over from the original engine in September 2015.