I'm transitioning from OSX to Windows 10. The transition is smooth except for one thing: The default image viewer in OSX, Preview, has more functionality regarding multiple folders.
In Preview, I can open a file from one folder and view it. I can open a file from another folder and view it as well. As I open a third, fourth, etc. file from different folders, thumbnails of the files I've opened appeared in a sidebar.
This is a screenshot of Preview in OSX. Notice the four thumbnails in the left sidebar. All four images are from different folders. One image is from Costa Rica; another from Guatemala; another from Honduras; and a fourth in a folder named "Flowers." I can add a fifth image by just double-clicking the file in Finder. Very simple.
So far I've used Windows 10's default Photo app, IfranView, Fast Stone Image Viewer, and Picasa. All are great apps...if you're viewing a set of images in the same folder. If you're viewing from different folders, they're not useful.