Counter-Strike

Counter-Strike (also known as Half-Life: Counter-Strike or Counter-Strike 1.6) is a tactical first-person shooter game developed by Valve. It was initially developed and released as a Half-Life modification by Minh “Gooseman” Le and Jess Cliffe in 1999, before Le and Cliffe were hired and the game's intellectual property acquired. Counter-Strike was released by Valve for Microsoft Windows in November 2000, and is the first installment in the Counter-Strike series. Several remakes and ports were released on Xbox, as well as OS X and Linux.

Source: TheGamesDB