Build 14D130a of OS X Yosemite 10.10.3 is available for developers from the Apple Developer Center, as well as the Mac App Store. Public beta testers can also get the update from the Updates section of the Mac App Store.

OS X 10.10.3 contains the new Photos for Mac app. The app will let you view, manage, and edit your iCloud Photo Library on your Mac, and will replace Apple's current iPhoto and Aperture applications when it launches to the public at some point this spring.