The Construct is a free software that allows you to link 360 photos into a virtual tour.
The Construct is a software that enables you to create virtual tours by linking 360 photos. The tours can be seen on the web (here) or through viewers such as Samsung Gear VR or Google Cardboard using theViewer app (Gear VR; Android; iOS). [As usual, please review the privacy settings before installing any app.]
TheConstruct is currently free when you sign up on their website, and according to the developer, the basic functionality will remain free, but they will charge for customization options in the future.
Thank you very much to Danny Mydlack for bringing this to my attention!