Counter Strike is the critically acclaimed and very popular PC game series, which began in 1998 as a Half-Life mod. There are several versions of the game, with 1.5 being the first to release on Steam. Currently three versions are available: the old 1.6 based on the first Half-Life engine, CS: Source based on the Half-Life 2 engine, and Global Offensive, which runs on a newer version of the engine and features matchmaking, weapon skins and stickers, new and remastered maps, and community servers together.
In Counter Strike, the Terrorists and the Counter-Terrorists fight with each other in several different game modes. These include Defuse in which the T's have to plant a bomb on one of two determined bombsites, and the CT's goal is to either kill them or defuse the bomb if they planted it. Another popular mode is Hostage, in which the T's defend two hostages and the CTs have to get them back to their spawning point. These modes are round-based: if a player has died, he has to wait until the next round to get back in the game. Several other, not competitive modes include Deathmatch, Arms Race and Demolition.
Global Offensive has a very active competitive scene with real prizes, events and parties centered around the game, while being easy to get into thanks to the matchmaking system based on skill levels. It is available on Steam just like the other two entries, and is the second most played game on the platform.