A 48-hour "secret access" period is now open for Age of Empires Online, letting all and sundry into the beta test before it closes back up again. Microsoft revealed this in an official release, which is perhaps not the best way to keep a secret, all things considered.
Until 1:01am PST on Saturday, you can get into the beta by heading on over to the Games for Windows Marketplace and 'buying' the free beta client. You'll need the Games for Windows Live client to download and play. Once the 48 hours are up, beta access will be closed again but the beta itself will still continue to run.
Ages of Empires Online combines the classic AoE strategy series with a persistent social-y world. It was initially developed by Robot Entertainment, but work is now lead by Gas Powered Games. The full game's due to launch for free through GFWL later this year as part of Microsoft's half-hearted campaign to "step up" its PC gaming efforts.