RawTherapee - RawTherapee is a free RAW converter and digital photo processing software.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
Darktable - darktable is an open source photography workflow application and raw developer.
PhotoFlare - Quick, simple but powerful Cross Platform image editor.
digiKam - Professional Photo Management with the Power of Open Source
PixBuilder - Free Photo Editing Software for PC