Counter-Strike is a modification (MOD) to the excellent game, Half-Life. It modifies the multiplayer aspects of Half-Life to bring to it a more team-oriented gameplay. Counter-Strike provides the player with an experience that a trained counter-terrorist unit or terrorist unit experiences. The MOD is team-based featuring one team playing the role of the terrorist and the other team playing the role of the counter-terrorist. Each side has access to different guns and equipment, as well as different abilities. Maps have different goals such as: hostage rescue, assassination, bomb defusion, Terrorist escape, etc. Weapons include the usual assortment of pistols, shotguns, assault rifles, sniper rifles, grenades, demolition devices. Each side has access to a different subset of weapons so for example only the counter-terrorist can use the M4A1, and only the terrorists can use the AK-47. We are confident that we've created a MOD quite unlike any other.
Quite possibly the most successful mod ever, it was nice to see it effectively become its own game. It's also nice to see that so many people across the world still play original CS even today, myself included.