Using HTML and JS works great and provides exactly the same interaction you'd see on the final product. I think trying to do anything else (unless you're extremely good at video processing) is insane.

I hear Framer(http://www.framerjs.com/) is pretty sweet.

Not easily. Adding a few layer groups that show different states often works well for simple things. HTML/CSS + JavaScript are great if the designer knows how to do this. The next best thing is something like Balsamiq workflows with a detailed textual description.

've heard of but haven't used: http://keynotopia.com/