"Team Fortress Classic, also known as Team Fortress 1.5 or simply TFC, is a team-based multiplayer first-person shooter video game developed by Valve Corporation. It is a remake of the Team Fortress modification for Quake, itself modified from Valve's GoldSrc engine. Team Fortress Classic was originally released for Windows on 7 April 1999 as a free addition to Half-Life. A standalone version was later released with Valve's Steam system in 2003. The development of Team Fortress Classic was led by John Cook and Robin Walker, the designers of the original Team Fortress modification.
The game was originally announced in 1999, powered by Valve's GoldSrc engine. The designers of the Team Fortress modification were contracted by Valve to develop Team Fortress 2, but initially remade their original work on Valve's game engine. The game itself involves a number of teams, each with access to nine classes, competing in a variety of scenarios such as capture the flag, VIP protection and territorial control. In June 2000, the game underwent a significant upgrade, adding new player character models and game modes. As of 2008, the game is one of the ten most played Half-Life modifications in terms of players, according to GameSpy."
Source: Wikipedia, Team Fortress Classic , available under the CC-BY-SA License.