DesktopShelves takes a refreshing approach to organizing files. It focuses on saving space on your screen while allowing you to always quickly access your files (via hotkey).
Everything is drag and drop. You can even drop text selections on a shelf and a new file is created automatically. Right-click and drag a file away from a shelf to insert its contents into another application such as Mail (great for keeping a "shelf" with frequently used mail templates, for example).
Updated on Aug 13 2019
Note: The downloadable demo is version 2.1.4; the version available for purchase on the Mac App Store is version 2.4.0.