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.