While you can learn anything you want for free online these days, or in person, some people learn best with interactive tutorials. For those people, I've provided this post to get you started.
Let me know if you know of any interactive tutorials I'm missing that teach something other than what is taught in the lessons below, that I should add to the list!
DataCamp (R, Python, SQL, Spark, Shell, Spreadsheets)
Learn Git Branching
Vim Adventures (game)
Codingegame (many languages, tied to games)
Unity 3d (for making games)
docker and containers
kubernetes - creating a cluster
Music / Ableton