id Tech 2 ▶ GoldSrc ▶ Source ▶ Source 2
Source 2004 ▶ Source 2006 ▶ Orange Box branch Source 2007, Source 2009/MP, Source 2013 (Xengine) ▶Left 4 Dead engine branch ▶ Alien Swarm engine branch ▶ Portal 2 engine branch (Titanfall engine branch) ▶ CS:GO engine branch (Strata Source) ▶ Dota 2 engine branch
Garry's Mod ▶ S&box
Quake Team Fortress ▶ Team Fortress Classic ▶ Team Fortress 2
