SuperJPG is described as 'Explorer style thumbnail and multiple image viewer' and is a Image Viewer in the Photos & Graphics category. There are three alternatives to SuperJPG for Windows, Mac and Linux. The best alternative is PureRef, which is free. Other great apps like SuperJPG are Kuadro (Free) and RefShelf (Free).
Kuadro is an image viewer that allows you to open as many windows as you want, lay them out as you need them and store those layouts for later.
It was designed to stay out of your way, and work around you.
Intuitive tool for viewing & managing reference images. Capture images from different sources, store them, provide access to any in one click. View images in always on top mode by default. Convenient for everyday use not only for CG artists.