Apple has just seeded the second beta of OS X 10.10.5 to developers. This comes two weeks after the first release. This update includes bug fixes and improvements. Other than that we’re not sure what’s new, which lis likely nothing much.
Developers can update to beta 2 in the Mac App Store > Updates > Software updates > OS X 10.10.5 beta 2. If you don’t have it yet you can download it for the first time from the Apple Developer Center.