How to find third-party photo extensions
As of now there only a few extensions for Mac OS X Photos. Many more will be rolling out in the near future. So the extensions available right now are:


BeFunky Express
Intensify
Tonality
Noiseless
Snapheal
Affinity Photo
Pixelmator
DxO Optics Pro
External Editors for Photos
Picktorial
Polarr
HayPhotos
Lochkamera