I’ll start by plugging Harvard’s free courses catalog as well as Udemy
Edit: Gonna add 2 more I remembered-
Blender - I wish I had more time to learn it, but I did start the infamous “Donut Tutorial” once!
Watch Cartoons Online - Lots of good older stuff!
Plug for Medito, which is a free non-profit for guided meditations. Not sure if the apps are open-source but still, they’re a good organization in stark contrast to the many other meditation companies that are very much for-profit.