What game was used to advertise Steam?

Counter-Strike 1.6 was used to advertise Steam because it was a highly popular and widely recognized first-person shooter game during its time, and utilizing it as a flagship title helped to attract and engage a large gaming community. By offering Counter-Strike 1.6 as a prominent game on the Steam platform, it showcased the capabilities and benefits of using Steam as a digital distribution platform for games, encouraging players to join and explore the diverse range of games available on the platform.