If you bought Half-Life in 1998 and ended up playing it until 2003, odds are you were a fan of Counter-Strike. The military shooter mod's first public beta began exactly ten years ago.

In Counter-Strike, players are split into two teams - Terrorists and Counter-Terrorists - and tasked with blowing up/defending an objective or rescuing/defending hostages. Its realistic gameplay - with one-shot kills and weapon recoil - were a stark contrast to other popular multiplayer games at the time like Quake that gave players rocket launchers and gobs of health. While no doubt many former players have moved on to newer military shooters like Call of Duty 4: Modern Warfare, there's still plenty of folks playing Counter-Strike to this day.

The mod evolved greatly over the years and was updated with the Half-Life 2 Source engine in 2004. You can get Counter-Strike or Counter-Strike: Source via Steam for $9.99 and $19.99, respectively. Counter-Strike: Condition Zero, a standalone version of the original mod with single-player missions, was released in 2004 and can also be found on Steam for $9.99.