Green Man Gaming is a discount digital games store. It sells some games with Steam codes and other games with its own GMG launcher called Capsule. It also allows you to trade in Capsule games for store credit.

Playfire is a gaming social network, very much like Steam Community, but it links your PSN, Xbox Live, Wii [via Xfire], and Steam accounts. You don't need your passwords, Playfire can only see what you already publicly reveal on those accounts.

GMG and Playfire merged last year. If you link your GMG and Playfire accounts together, then you can get four free games this weekend. These games are tied to your GMG account, not Steam.

The Grand Playfire & GMG Giveaway

Zombies
Ninja Blade
Unstoppable Gorg
Superstars V8 Next Challenge

I already had a GMG account, so I setup a Playfire account today. It was painless. I don't think you even need to link your actual Steam account. You could probably throw any random junk in the "Steam ID" spot and it'd think you've linked an account.

Why would you want to gain four games you'll never play? Easy. These are Capsule games, so in the near future you'll be able to trade them in for store credit at GMG [probably only 50 cents per game], and use it to buy a game you actually want. I dunno, like the Skyrim Dragonborn DLC or something.