In "Free Roam" the vast and expansive open world of Red Dead Redemption's single player offering serves as the game's "lobby," allowing for up to 16 players to explore the game world, hunt game, take out the lawless, and even fight each other, either as a posse ranging from 2-8 players or alone. Free Roam even offers level based progression that earns players new mounts, weapons, characters, titles and more.
Red Dead Redemption will launch on the PlayStation 3 and XBOX 360 on May 18. Unfortunately, a PC version has not been announced, but many of Rockstar's titles do tend to appear on the PC, so there is yet hope!