Counter-Strike is an objective-based, multiplayer tactical first-person shooter. Two opposing teams—the Terrorists and the Counter Terrorists—compete in game modes to complete objectives, such as securing a location to plant or defuse a bomb and rescuing or guarding hostages. At the end of each round, players are rewarded based on their individual performance with in-game currency to spend on more powerful weapons in subsequent rounds. Winning rounds results in more money than losing and completing objectives such as killing enemy players gives cash bonuses. Uncooperative actions, such as killing teammates, results in a penalty.
Counter-Strike: Source was the first publicly released game by Valve to run on the Source engine. Counter-Strike: Source was initially released as a beta to members of the Valve Cyber Café Program on August 11, 2004. On August 18, 2004, the beta was released to owners of Counter-Strike: Condition Zero and those who had received a Half-Life 2 voucher bundled with some ATI Radeon video cards. While the original release only included a version for Microsoft Windows, the game eventually received a port to OS X on June 23, 2010, with a Linux port afterwards in 2013.
Counter-Strike is considered one of the most influential first person shooters in history. The series has a large competitive community and has become synonymous with first person shooters.[32] As of August 2011, the Counter-Strike franchise has sold over 25 million units.

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The data comes from Wikipedia or steam db. CS will always be the number one game. If anyone leaves a dissatisfied message, I will kick your ass.