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!
Darktable - darktable is an open source photography workflow application and raw developer.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
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.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.