Neural Networks, Deep Learning, Machine Learning resources

I have come across a few great resources that I wanted to share. For students taking a machine learning class (like Northwestern University's MSDS 422 Practical Machine Learning) these are great references, and a way to learn about them before, during, or after the class. This is not a comprehensive list, just a starter. There is a free online textbook, Neural Networks and Deep Learning. There is a great math visualization site called 3Blue1Brown and they have a YouTube channel.