Valve Software (now known simply as Valve) released their first game, a Quake 1 engine based first person shooter called Half-Life. It's now considered one of the greatest PC games of all time and its success has launched Valve's work with mods like Counter-Strike, the sequel Half-Life 2, their Steam content delivery system and others, including this week's release of Left 4 Dead.
If you have never played the original game before, this is a perfect time to do so. Valve is celebrating Half-Life's 10th anniversary by putting the game on sale via Steam for just 98 cents. Normally the game sells separately for $9.99 The sale expires on Friday at noon PST.