Apps similar to Photo Sphere Viewer include FSPViewer, which is free. Other options are Panorado, SphereView, lux and Pannellum. In total there are eight apps like Photo Sphere Viewer for Windows, Linux, Mac, the web and Android.
FSPViewer is a 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.
Italy
EU
Panorado is a comfortable image viewer with special support for panoramic and HDR images, with browsing capabilities and some very useful imaging tools.
ItalyEU
GermanyEU
Pannellum is a lightweight, free, and open source panorama viewer for the web. Built using HTML5, CSS3, JavaScript, and WebGL, it is plug-in free. It can be deployed easily as a single file, just 15kB gzipped, and then embedded into pages as an <iframe>.
United States
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.
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.
ItalyEU
Based on PURE technology, ImmerVision's panoramic image viewers combine superior performance capabilities with optimal viewing ease on either a standard office PC monitor or a pocket computer. The "immersive" panoramic experience is no longer limited to desktop...
Canada