Obsidian Entertainment, best known for their work on Star Wars: Knights of the Old Republic II and Fallout: New Vegas, are currently working on South Park: The Stick of Truth and aiding InXile Entertainment with Wasteland 2, but they're also working on something secret, something they call Project X.
Some speculation (a href="http://www.shacknews.com/article/75689/obsidian-hints-at-a-dungeon-siege-sequel">Shacknews</a>) suggest the four on the website would indicate a Dungeon Siege 4 (Obsidian developed the third game), but that seems highly unlikely. There is also some speculation on the Obsidian forums that this may be tied to the plans for video games based on Robert Jordan's Wheel of Time books.
However, the most likely scenario is that this is a new original project designed by Obsidian Entertainment themselves. Likely a fantasy RPG given the wording on the teaser site, and we're likely going to be told more about it very soon.