Hugin is a free cross platform open source panorama maker, which also has the power to make 180x360 degree photospheres.
Ranked in these QuestionsQuestion Ranking
Pro Cross platform
Linux, FreeBSD, Mac, and of course, Windows.
Pro Free and open source
Fully free to use, no demo or other strings attached.
Con Learning curve
Chances are, you will probably have to do a certain amount of research before you succeed in making your first photosphere.