I have over 4 years experience with Krpano. I started with immervision, made a sideturn to FPP and ended using Krpano. In my opinion it’s the best viewer out there.
Backbone.js, RequireJS, jQuery, Underscore, Mootools or Prototype.js. With the increase of user interaction and complexity shifting from backend to frontend, I picked up several javascript libraries to get the job done.