digiKam - Professional Photo Management with the Power of Open Source
Priime - Edit photos with the styles of the world's top photographers. Smart suggestions, fast editing, and inspiring collections.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
Filters for iPhone - Transform your photos. 800+ filters and effects. Just 99¢.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Dubble - Take a picture and randomly mix it with anyone in the world