The Steam and Xbox releases of Counter-Strike are commercial standalone versions of the game, updated with a newer GoldSrc engine build. However, they omit the extra modifications which were available in the Half-Life: Counter-Strike retail releases that are not Counter-Strike itself.
The Linux and Macintosh PC versions were never available separately. When they were released, Counter-Strike could only be bought as a compilation pack containing both Counter-Strike: Condition Zero and the original Counter-Strike. However, existing players who only owned Counter-Strike thus received it for the additional platforms for free, even if they did not own the original Counter-Strike: Condition Zero or never bought the compilation pack.
