nomacs is a free, open source image viewer, which supports multiple platforms. You can use it for viewing all common image formats including RAW and psd images.
XnViewMP is a free software to view, organise, convert graphics and photos files or to create slide show, contact sheet, HTML pages.
Gwenview is an image viewer for KDE. It can load and save all image formats supported by KDE, but Gwenview can also browse GIMP files (*.xcf). Gwenview does not try to replace your favorite image editor, so it only features the most simple image manipulations: rotation and...
gThumb is an image viewer and browser for the GNOME Desktop. It also includes an importer tool for transferring photos from cameras.
Eye of GNOME is the official image viewer for the GNOME Desktop environment. With it, you can view single image files, as well as large image collections. The Eye of GNOME supports a variety of image file formats.This app doesn't have any features at the moment.
feh is an X11 image viewer aimed mostly at console users. Unlike most other viewers, it does not have a fancy GUI, but simply displays images. It is controlled via commandline arguments and configurable key/mouse actions.This app doesn't have any features at the moment.
Xee is an streamlined and convenient image viewer and browser. It is similar to macOS's Preview.app, but lets you easily browse the entire contents of folders and archives, move and copy image files quickly, and supports many more image formats.