There are a few free ones but some of them have limitations such as limiting the number of tours you can do before paying. Some examples are Webobook, Lapentor, Marzipano, Makevt and OpenSpace3D.
Togotiki has a free trial and gives demo/training sessions. It is easy to use and does both 360 Virtual Tours and Interactive Videos. It is a single tool for both your video and 360 content allowing you to save time and money. You can easily blend your video walk-through with 360 content - giving your customers a better view of your property.