In both appearance and features, Photos for OS X is designed to mimic the Photos app bundled in iOS. The tie may be more than just superficial. According to Six Colors, early evidence uncovered by developers suggest that Photos for OS X uses UXKit, which is similar to UIKit on iOS.
The app provides four different ways to interact with your photos and videos including Photos, Shared, Albums, Projects and Import. Similar to its iOS counterpart, the Photos view groups photos into Years, Collections, and Moments, allowing you to browse your photos according to when and where they were taken. The app also has a similar Shared view that displays your shared photo streams and any streams other people have shared with you.
The aptly named Albums view display your photos grouped into albums that you created as well as several pre-configured albums such as Last Import, Favorites, Panoramas and more. Photos for OS X also includes a Projects section for saving your books, cards, and calendars as well as an Import tab that shows images and videos that can imported from a camera or other external media.
More than just a viewer, Photos for OS X includes detailed EXIF data on images and an editor that provides tools like Enhance, Rotate, Crop, Filters, Adjust, and Retouch. Not suprisingly, Photos for OS X integrates with iCloud Photo Library with an option to store your original files on your local machine.
Photos for OS X is only available in the developer version of OS X. It is expected to debut later this spring when the free Yosemite 10.10.3 update is released to the public.