What are some great topics for presentation/discussion at dev meetings?

My company holds weekly developer meetings, and each week we like to have a new software development topic for discussion. We've done topics such as "vi for beginners", "Android Wear and You", and "Unit Tests!". Looking for suggestions on fresh, new topics. They don't even have to be super technical, as long as the topic is something that you think a software developer should have exposure to! Thanks!