The second announcement form Valve. Now speculations of the third announcement is that it could be Half-Life 3, playable only on the new Steam OS.

Valve designed a high-performance prototype that’s optimized for gaming, for the living room, and for Steam. And it’s also completely upgradable and open. This year they’re shipping just 300 of these boxes to Steam users, free of charge, for testing. You can make yourself eligible to get one.

Link to Official Site (SteamOS)

Link to Steam other Announcments

Beginning in 2014, there will be multiple SteamOS machines to choose from, made by different manufacturers.

THE HARDWARE BETA ELIGIBILITY QUEST:
Before October 25, log in to Steam and then visit your quest page to track your current status towards beta test eligibility
1. Join the Steam Universe community group
2. Agree to the Steam Hardware Beta Terms and Conditions
3. Make 10 Steam friends (if you haven’t already)
4. Create a public Steam Community profile (if you haven’t already)
5. Play a game using a gamepad in Big Picture mode