http://www.joinfear.com/us/
It's the multiplayer portion of FEAR, along with new gamemodes, maps, and 12 weapons.
Had a LOT of fun with this game last year.. multiplayer is a blast, one of the only games to get melee combat right, plus it exaggerates skill level rather than diminish it like in later versions of CS. It's not uncommon to see scores of 40:1. You can do crazy things like shoot and detonate the grenade out of someone's hand as they're throwing it. Hopefully the mp community will pick up again with the influx of new players.
It's rare to see companies doing this sort of thing nowadays. Go Sierra!