PicPodz (On the Mac App Store)
9.9.15: Added a small guide photo when no other photos are in the frame.
PicPodz3D is another desktop photo app/widget for OS X (10.10+) Simply drag photos into the window. The window can be re-sized to meet your needs. Photos swirl around in a sphere. Click the photos you want to bring to the front, or turn on automatic mode with the “Z” key.