GPicView vs nomacs

When opening multiple images at once it opens every single picture in a separate window.

It has all the necessary functions that you can reasonably expect from a lightweight image viewer: you can view all the image files in a directory, rotate and save them.

And still you can browse all images in a directory.

No cramped toolbars or large icons; the UI is cohesive, minimal and keeps out of your way.

Starts very quickly and has a small memory footprint.

It is important if you have to work with photos of documents and want to cut off the background on which you made photos.

Can display thumbnails in a strip or a zoomable grid as well, also has hotkey for both of these. Opening a folder is one of the main actions on the toolbar!

Has builds for Windows, Mac and Linux.

Often used folders (e.g., screenshots) can be quickly accessed.

Has tools for applying conversions etc. to many files at once.

Unlike most other image viewers.

Such as WebP, AVIF, etc.

This feature is called Synchronization. With the synchronization it is possible that multiple viewers perform the same action (like panning, zooming, etc.). This feature is useful when comparing two images. See more here.