PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
PhotoFlare - Quick, simple but powerful Cross Platform image editor.
Corel AfterShot Pro - Say hello to Corel AfterShot Pro 3, the world’s fastest photo workflow tool! Edit your photos up to 4x faster than Lightroom so you can spend more time behind the camera. Download a free 30-day trial today!
showFoto - ShowFoto is the standalone image editor of the digiKam project.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!