Darktable - darktable is an open source photography workflow application and raw developer.
digiKam - Professional Photo Management with the Power of Open Source
Adobe Lightroom - Adobe Lightroom is a family of image organization and image manipulation software.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Pixelmator - Pixelmator is an image-editing application for Mac and iPad.
IrfanView - IrfanView ... one of the most popular viewers worldwide.