Steam uses a “Content Description Record” to distribute lists of their games and their information to the Steam clients across the world.
It is possible to access these records without actually having a Steam client, so Marlamin made a parser for this. It downloads an XML file every hour and throws it into a database. The result is having an up to date database of Steam Apps and Subscriptions.
This tool by Marlamin have been used in past to leak information about Humble Indie Bundles. All of these leaks turned out to be true with the Bundle in question launching just within days of leak.
Now an interesting CDR have appeared toady and well check its content yourself by clicking here.
So Steam for Linux Beta will be launched sooner than you think. Here is another proof from Steam CDR maintained by The Bronasium.
Thanks to mr.Ofen