LightGallery!

nomacs is a free image viewer for windows, linux, and mac systems, which is licensed under the GNU Public License v3. nomacs is small, fast and able to handle the most common image formats including RAW images. Additionally it is possible to synchronize multiple viewers. A synchronization of viewers running on the same computer or via LAN is possible. It allows to compare images and spot the differences (e.g. schemes of architects to show the progress).

JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images. On-the-fly image processing is provided - allowing to adjust typical parameters as sharpness, color balance, contrast and local under-/overexposure.

ImageGlass is a simple picture viewer with which you will be able to display your image collection in a very similar way to the one that Windows provides by default, but with some additional functions. This application will allow you to better manage your pictures thanks to the options it includes and the extension it enables to install for adding more functions and widening its possibilities.

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 mirroring, but can be extended by installing KIPI plugins. When working with JPEG files, Gwenview performs lossless manipulations.

Its minimalistic interface provides more screenspace for your images. Among its features are:

PhotoQt is a simple, yet powerful and good looking image viewer, written in Qt, published as open-source, and completely free.Photo comes with a variety of features. Most features you would expect from a image viewer should be there.All features of PhotoQt are very easy to use. Should you happen to be confused about some feature, have a look at the settings. Pretty much everything can be adjusted in PhotoQt, and every setting comes with a short explanatory text.

Xee is a lightweight, fast and convenient image viewer and browser. It is designed to be a serious tool for image viewing and management, with a sleek and powerful interface.

QuickViewer is a graphic image viewer for comfortable browsing of many images.

You can use the Photos app to view or edit photos and videos in your Pictures library and on OneDrive, and to import photos and videos. The Photos app includes a wide range of editing options to enhance your photos, from automatic fixes to advanced adjustments. After you've finished editing your photos and videos, you can then share them with friends and family without leaving the app.

GPicView is a simple and fast image viewer with low memory usage. This little program is not aimed to be powerful or feature-rich. Its aimed to replace the default image viewer of current desktop systems. Fast-startup, low memory usage, and simple user interface make it a good choice for default viewer.

Ristretto is a fast and lightweight picture-viewer for the Xfce desktop environment.