I'm going by concepts:

Learning how to apply clean architecture (ref: Robert C Martin) when using a large framework like rails/django. Learning ruby, rails, and django (already quite familiar with python. Been using flask for everything I do so far).

Building a real time application. Learning meteor and how to apply TDD with meteor.

Building a front end heavy single page application. Relearning HTML and CSS properly. Still deciding whether to use React or Ember. Ember's documentation is bad but I've already put up my hand to help improve it. I really want to help. But react is just looking really good and it's docs are stellar. To the point that I feel like I'd be missing a bus if I ignored learning it. Will probably toss a coin on that.