- fast.ai: offers free courses for practical introductions to machine learning and neural networks. (Disclaimer: I haven’t gone through the courses yet, but have heard lots of great things about them, and plan on going through them at some point.)
- Learn Git Branching: a visual and interactive introduction to the most common and useful git commands and concepts.
- The Missing Semester of Your CS Education: a series of freely available online classes at MIT, intended for filling in gaps in knowledge for CS (Computer Science) students.