Is there a compilation of ML/AI free online courses available for beginners?
There are a lot of Machine Learning Courses on the internet and also a lot lists which ranked this courses: One of this lists you can find here. This is a good list, when you want to start with supervised (Linear Regression, Neural Nets, SVM, ...) and unsupervised (K-Means-Clustering, PCA, ...). I would prefer to start with the Coursera course from Andrew Ng, with which I started too.Here he get started with Octave instead of Python which is great for beginners.
Furthermore there is also one more field of machine learning, besides unsupervised and supervised learning. This field is called reinforcement learning. About that topic you will find much less courses, but still enough. One good start for this is David Silver's course or Richard Sutton's Book Reinforcement Learning: An Introduction