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!
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.