For a game similar to 'Counter-Strike Online' ...

Video Game genre...

Action adventure RPG Shooter Racing Platform Strategy Fighting Simulation puzzle MMORPG Music Arcade Fantasy Eroge Sports game Visual novel Survival horror Third-person shooter First-person shooter

On following platform...

Microsoft Windows Sony PlayStation 2 Xbox 360 Sony PlayStation 3 Sony PlayStation iOS Nintendo Wii Nintendo DS Mac OS X Amiga Super NES PlayStation Portable Xbox GBA Nintendo Entertainment System Sego MegaDrive Android GameCube GNU/Linux Game Boy Saturn PlayStation Vita Nintendo 3DS Nintendo 64 Sega Dreamcast Game Boy Color Sony PlayStation 4 Wii U Sega Master System Sega Game Gear

... I can play

Left 4 Dead

Left 4 Dead

2008  First-person shooter - Mac OS X Xbox 360 Microsoft Windows - multiplayer  
Valve is famous in the gaming community for coming up with some of the best shooting game titles throughout the decades and Left 4 Dead is one of them. If there is someone you can trust to make a good FPS it’s the guys that already created Counter-Strike and Half-Life. Left 4 Dead is one of the best modern horror survival shooters, a game with plenty of zombies and mutants for you to shoot up. Step foot in infected cities and clean them up with the power of the good old bullet through a barrel!
 Get game Left 4 Dead
Left 4 Dead - Wikipedia Left 4 Dead is a cooperative first-person shooter video game with survival horror elements, developed by Turtle Rock Studios and Valve Corporation. The game uses Valve's proprietary Source engine, and is available for Microsoft Windows, Xbox 360 and ...   more on Wikipedia
Quake II

Quake II

1997  First-person shooter - Sony PlayStation GNU/Linux Nintendo 64 Xbox 360 Microsoft Windows - multiplayer  
Time for a trip down memory lane with Quake II, a first-person shooter that was a groundbreaking creation by id Software at its time! Shed tears of nostalgia as you battle for survival against a vicious race of aliens!
 Get game Quake II
Quake II - Wikipedia Quake II is a first-person shooter video game developed by id Software and published by Activision. It is not a direct sequel to Quake; id decided to revert to an existing trademark when they were unable to agree on a new name that did not violate an ...   more on Wikipedia