It's...a site about patents! It'll be in private beta for ~2 weeks, and then you'll hear a lot more about it.
It's in private beta right now like every other new site because we want to have time to set up the site, make sure everything is working right, etc. before the public launch.
Rory's answer does a good job explaining why it didn't go through the normal Area 51 process and gets a special design, but for the most part the site will work like any other SE site and join the network publicly in a couple weeks.
In the meantime, if you're interested in the US Patent system feel free to hop in. Because it skipped Area 51, anyone is welcome to join the private beta.