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.