Kifi. They just launched a few weeks ago. I wish I was an investor -- I love their concept and think it will get popular fast.
The overall flow is simple:
Their implementation of this simple concept is what makes them valuable.
They launched in November after being accelerated in Amsterdam. They have created a platform they describe as "Playlists for learning", and I think they tackle a really interesting area of education/learning, and I can see some very strong monetisation cases for the future.
*disclaimer - Whilst I don't know the founders, I do know one of the team, but I am neither advisor nor investor, just a happy user.