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!
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Corel AfterShot Pro - Say hello to Corel AfterShot Pro 3, the world’s fastest photo workflow tool! Edit your photos up to 4x faster than Lightroom so you can spend more time behind the camera. Download a free 30-day trial today!
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
GIMP - GIMP is a multiplatform photo manipulation tool.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.