Age of Empires Online, its two-faction freemium revamp of the series. The Egyptians will oppose the red team (obviously), which is hellbent on expanding Greece's borders across the whole world. Stay tuned -- we'll be posting our preview of the Egyptians gameplay later today.
Additionally, Microsoft has detailed some of the social and MMO features planned for AoE Online, which center on players' capitol cities, and has confirmed Game for Windows Live support (including Achievements). The capitol city -- you can have two; one each for your Greek and Egyptian civilizations -- will be the player's persistent headquarters, used to access quests and rule over the empire, and will function as a travel destination and interaction point for other players.
Aside from marveling at your flower gardens (think of your capitol as "FarmVille Lite"), visiting players can join up with you in co-op missions or simply shop at your unique store fronts. Paying players will have incentive to encourage visitors to shop, too, as the premium faction upgrade adds kickbacks: You'll receive in-game currency for purchases made from your stores. Microsoft's detailed "cheat sheet" of the differences between free and paid play is posted after the break.
Importantly, Microsoft has said it won't "nickel-and-dime" players -- upgrading from the free-to-play version of a faction is done through a one-time premium add-on, the "Premium Civilization Pack." Microsoft has not yet announced pricing for the upgrades. Age of Empires Online is currently in beta and should be released this year.