digiKam - Professional Photo Management with the Power of Open Source
Photos on macOS - Photos keeps your images organized and accessible. Rediscover favorite shots with Memories. Access them on your devices with iCloud Photos.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
StudioLine Photo Basic 4 - StudioLine Photo Basic 4 is a sophisticated image development tool that allows photo editing and multiple presentation options for personal usage.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
IrfanView - IrfanView ... one of the most popular viewers worldwide.