It can also read many other file formats: TIFF (8,16, 32 bits), JPEG, PDF, AVI, MPEG and QuickTime.
OsiriX is complementary to existing viewers, in particular to nuclear medicine viewers.
It is actually the free version of an expensive DICOM viewer. Horos is an open source DICOM viewer for Mac.
PostDICOM is one of the best DICOM viewers that offers almost all of the above features.