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!
SageThumbs - SageThumbs is a powerful shell extension allowing to preview enormous amount of image formats...
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Icaros - Icaros is a collection of lightweight, high quality, Windows Shell Extensions
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
FastPreview - FastPreview was created in need of a usable ...
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.