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!
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Metastream - Watch streaming media with friends
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.
StreamParty - StreamParty is a watch communiry, that allows you to watch video streams in sync with the people you care about, on multiple services.