1. Counter-Strike Online is a Free FPS game, you don't have to pay even 1 cent to play this game, unlike Steam, Steam needs a retail CDKEY to active your Counter-Stike 1.6 on the Steam platform, without the keys, you are not allowed to play Counter-Strike 1.6.
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2.There are more guns , Player Models and maps than Counter-Strike 1.6 in Counter-Strike Online.
3.Team Deathmatch , Deathmatch and bot are built-in the game, you don't have to install plugin and extra file to allow/play it in Counter-Strike Online.
4.Built-in Ranking and Clan system.