Apple's annual developer conference in San Francisco.
Apple Releases OS X Mavericks Developer Preview 2
The second iteration of the OS X Mavericks beta carries a build number of 13A497d, while the original version released on June 10 was build 13A476u.
Mavericks includes features like a tabbed Finder, new full screen dual monitor capabilities, and Safari improvements. Developers can receive the update via the Software Update tool in the Mac App Store.