While Photos is streamlined and zippy compared to iPhoto, its stripped-down approach can be confusing. PowerPhotos takes some of the shock out of Photos for OS X by helping bridge the gap between old and new. Fat Cat Software’s app offers assistance in migrating iPhoto libraries, managing (and merging) multiple Photos libraries, and offers a different way of viewing images and videos. It’s more flexible, to be sure.
When launched, PowerPhotos shows—under an Operations listing—Migrate iPhoto Libraries, which can also be selected later from the File menu. This lists all iPhoto libraries that it can find via Spotlight; you can add others manually.