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!
PhotoTime - Automatic face sorting & keywords tagging for your photos
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Piwigo.org - Manage your photo collection with Piwigo. Piwigo is open source photo gallery software for the web. Designed for organisations, teams and individuals.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Facial Recognition by FB - Get notified if someone tries to use your photo on Facebook
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.