Darktable - darktable is an open source photography workflow application and raw developer.
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
RawTherapee - RawTherapee is a free RAW converter and digital photo processing software.
Pixelmator - Pixelmator is an image-editing application for Mac and iPad.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Pixlr - Pixlr® makes it easy to transform everyday images into stunning works of art.