It comes from Neal Stephenson's book The Diamond Age. (Although the ractives in The Diamond Age are quite a bit more powerful than ours.)
Do ractives work on mobile?
There are some UX improvements to be made, but yes, ractives should be fully functional on mobile. Check the Mobile section of the Authoring guide for tips on making sure your ractives are mobile-friendly.
Can ractives be uploaded to YouTube/Twitter/etc.?
No, you will have to host them yourself. But you can easily make an MP4 recording of a ractive and upload that to social media for discoverability, and then provide a link to the interactive version.