Ask HN: What are some great online learning resources available for free?

What are some great online courses and learning material to pursue as I am now spending more time at home in times of COVID-19?

I am looking for recommendations of specific courses or programs. And not learning platforms in general. It could be courses, interactive learning, educational games, or other forms.

I am interested in a wide variety of topics. For example computing, machine learning, math & statistics, leadership & organisation, economics, psychology, etc. As long as the material is great!

Please provide some reasoning for your suggestion.

Thanks :)