SAOImage DS9 is an astronomical imaging and data visualization application. DS9 supports FITS images and binary tables, multiple frame buffers, region manipulation, and many scale algorithms and colormaps. It provides for easy communication with external analysis tasks and is highly configurable and extensible. DS9 is a stand-alone application that requires no installation or support files. It supports advanced features such as multiple frame buffers, mosaic images, tiling, blinking, geometric markers, colormap manipulation, scaling, arbitrary zoom, rotation, pan, and a variety of coordinate systems.
skyviewer is an OpenGL-based program to display HEALPix-based skymaps, saved in FITS format files. The loaded skymaps can be viewed either on a 3D sphere or as a Mollweide projection. In either case, realtime panning and zooming are supported, along with rotations for the 3D sphere view, assuming you have a strong enough graphics card.