As Gearbox used their work to develop the Xbox version of the original Counter-Strike, Ritual completely re-made the game into an original 20-level single-player campaign (with a secondary multiplayer mode).
The main single-player campaign of Counter-Strike: Condition Zero is the Tour of Duty mode, in which players play Unlike the other Counter Strike games, Condition Zero offers a single player mode which is basically the same as the multiplayer version of the game only your teammates and the opposing team are replaced with AI or Bots.
Using steam as your gaming platform allows you to install the game you purchase / free games just by downloading from the platform.
Counter-Strike: Condition Zero is a modern-military first-person shooter developed by Valve (in collaboration with Rogue, Gearbox, Ritual, and Turtle Rock) and published for the PC by Valve (on Steam) and Sierra (on retail) on March 23, 2004.
They enhanced the AI of the original Half-Life to create the initial bot AI.