OS X Yosemite 10.10.3 Update:
The OS X Yosemite 10.10.3 update is recommended for all Yosemite users. It improves the stability, compatibility security of your Mac, and contains the new Photos app.
All new for OS X, Photos automatically organizes your photo library and helps you perfect your photos with comprehensive editing tools. You can also store your photos and videos in the cloud using iCloud Photo Library, and access them on all your devices.
Photos lets you:
● Browse your photos by time and location in Moments, Collections, and Years view
● Navigate your library using convenient Photos, Shared, Albums, and Projects tabs
● Store all of your photos and videos in iCloud Photo Library in their original format and in full resolution
● Access your photos and videos store in iCloud Photo Library from your Mac, iPhone, iPad, or iCloud.com with an web browser
● Perfect your photos with powerful and easy-to-use editing tools that optimize with a single click or slider, or allow precise adjustments with detailed controls
● Create professional-quality photo books with simplified bookmaking tools, new Apple-designed themes, and new square book formats
● Purchase prints in new square and panoramic sizes
Developers can get OS X 10.10.3 via the Mac App Store and Mac Dev Center.