‘Limoo’ is an open-source, QT 5 (user interface designer) based image viewer for GNU/Linux users who have a thing for minimalist & a bit fancy looking applications. It is however, is merely an image viewer and is not an image manager, like Shotwell.
It lets you browse through folders (with thumbnails/previews) & you can set images as the desktop background (worked perfectly in ‘Unity’), Cut/Copy/Rename/Delete/Rotate, set an image as the background (cover) of the application window, view simple details (Size, Dimensions & the Name) and open an image with a different application.
Any changes that you make (deleting an image or a folder in your file-manager, for instance) gets instantly updated on the application window. As mentioned in the beginning, it is very minimal and does not contain a menu, and all the above features are only shown when you right-click on an image (right-clicking again re-hides them), though the ‘Configure’ buttons allows a few customizations.
A different menu is shown if you right-click on an empty space, by using which you can create a folder (an actual folder on the currently opened location), paste images into it & open the location in your file-manager as well.
It is also consumes a reasonable amount of RAM when running & hung-up (most of the time) while trying to ‘update’ the screen accordingly after I made a few changes through the file-manager. But it is a fresh application and these bugs hopefully will be addressed in the future releases (Update: According to the author, this is now fixed).