OS X Mavericks Developer Preview 3 Build: 13A510d Available
But it's only for registered Mac developers. The pace of Mavericks development is increasing with Apple pushing out their 3rd build in as many weeks. Testing on network migration, keychain and a couple of third part apps are up for testing on this Mavericks build.
For those who have legitimate access to OS X Mavericks you might be interested in our guide on How To Install OS X Mavericks From A USB Drive