Good companions build the brand on Facebook

What exactly is Assassin's Creed: Project Legacy? Well, it's a Facebook game, but those who play it also get rewards when they move on to its big brother, the forthcoming Assassin's Creed: Brotherhood on other platforms. And assignments can be created in Brotherhood and then completed in Project Legacy, earning rewards in both games.

"We hope to create a virtuous cycle between the Facebook game and the Brotherhood game, meaning that I don't have to leave that game experience," Chris Early of Ubisoft told the Financial Times.

In another example of "companion gaming", Ubisoft says it will launch a Facebook version of CSI later this year. The company has sold more than five million units of the video-game version of the TV drama worldwide. In CSI: Crime City on Facebook, players will fight crime, and if they buy CSI: Fatal Conspiracy — the latest version of the game — they can become an elite investigator and get special laboratory items to help in their attempts to solve crimes.