FSPViewer is described as 'free viewer for spherical (equirectangular) panoramic images. It is designed for viewing local (hard-disk, network or CD) high resolution panoramic images at full screen and with very high image quality' and is an app in the Photos & Graphics category. There are five alternatives to FSPViewer for a variety of platforms, including Online / Web-based, Mac, Windows, Linux and Windows Mobile. The best alternative is Pannellum, which is both free and Open Source. Other great apps like FSPViewer are PhotosphereViewer.net (Free), PPV360HD (Paid), Panini (Free, Open Source) and PURE Player (Free).
PhotosphereViewer.net is a free service to view your and other people's Android Photospheres without having to use an Android smartphone, tablet or the need to upload spheres to Google Views, Google Plus or Google Maps. It's easy, fast and secure.
PPV360HD is an Android and Windows Desktop application designed to view 360-degree panoramic photo with equirectangular or cylindrical projection, at very hi-res resolution. The Android version can be executed on all smartphone or tablet with OS Android version from 2.0.
Panini is a visual tool for creating perspective views from panoramic and wide angle photographs. More than a pano viewer, more than a view camera, with features of both. For Linux/Unix, Win32, and Mac systems with OpenGL 2.0 +