I love numbers and math, a lot of people don't and they should be warned that this post is almost exclusively about math.
I've been taking a Game theory course online through Cousera and it has been very interesting. Game theory is not actually about making board games or video games, it is a discipline that models strategic interactions of almost any kind. I'm not done with this course yet and don't want to start making posts about it until I have a better understanding of the subject. However the course has reminded me of a lot of the classes I took in college and a couple of the most interesting theories that I found there.