Polarr Photo Editor 3 - The most powerful photo editor in the web.
digiKam - Professional Photo Management with the Power of Open Source
Fenetre App - Picture in picture for your mac.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
Darkroom 2.0 for iOS - The photo editor for enthusiasts, rebuilt from the ground up
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.