nomacs

Nomacs is a free, cross-platform image viewer. You can use it to view all common image formats, including RAW and PSD images.

It offers transparent widgets that display and additional information such as thumbnails, metadata or histograms. It is able to view images in ZIP format or MS Office files that can be extracted to a directory. Metadata stored with the image can be displayed and you can add annotations to the images. A thumbnail preview of the current folder is included, as well as a File Explorer panel that allows switching between folders. Within a folder, you can apply a file filter so that only images whose file names have a certain string are displayed. Activating the cacher allows instant switching between snapshots.