https://www.macworld.com/article/2773700/powerphotos-3-review.html
PowerPhotos 3 review: Time-saving Apple Photos tool for power users on the Mac | Macworld
May 12, 2025 - Powerhouse app lets you manage and work natively with multiple Photos libraries at once, adding capabilities lacking in Photos for macOS.
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https://sixcolors.com/post/2015/11/powerphotos-merges-photos-11-libraries/
PowerPhotos merges Photos 1.1 libraries – Six Colors
Six Colors by Jason Snell, Dan Moren and friends
six colorspowerphotosmerges