XnView MP stands for Multi Platform = it is available for Windows, Linux and MacOS. It is a continuation of the older XnView Classic. In my opinion it is a great alternative to Windows photos app or any Linux image viewer that comes preinstalled. I even think it is an alternative to IrfanView. It is really fast and simple to use, supports more than 500 image formats, has built in folder browser, image converter, editor... AND MORE!
TinType by Hipstamatic - Create vintage self portraits w/ Hipstamatic's new photo app
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Session - Complete photo session booking platform
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Oggl - Discover, create, & collect beautiful photos by Hipstamatic
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.