Team Fortress 2 was incapable of being developed.
Valve hired the developers of the Team Fortress mod to develop Team Fortress Classic using its GoldSrc engine (used in their 1998 game Half-Life) to promote the Half-Life software development kit
 Running up to Half-Life 2's release in 2004, Valve's Doug Lombardi claimed that Team Fortress 2 was still being developed and news of its release would come after that of Half-Life 2

