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!
Powerphotos - PowerPhotos lets you organize your Photos libraries on the Mac. You can split a library into smaller ones, merge libraries together, find duplicate photos, and more.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Monument Backup and Organization Device - Effortlessly store and manage all of your photos.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
digiKam - Professional Photo Management with the Power of Open Source
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.