Microsoft's "Project S", a secret strategy game that we uncovered earlier today, isn't a Halo title. It is, however, being worked on by by former Age of Empires developers.
Robot Entertainment, a studio that was formed by ex-Ensemble staffers following the closure of the venerable PC developers, is the team responsible for "Project S", whose launch screen you can see up top there.
It's not Halo. The game's other codename, Spartan, appears to be its actual name, with the splash screen showing a cute little Greek warrior. As for what type of game it is, that we don't know; the original reports said it was a "ground-breaking strategy game", though from the load-up sequence terminology - which has quests, units and crafting - we could guess it's got some RPG elements to it as well.
Robot's website - which coincidentally relaunched today - also mentions that the studio is working on a game for Microsoft Game Studios.