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!
This is a great thread!
Not foss, but PortSwigger Burp Community
I know its a major security tool widely used but it bugs me it’s not open sourced
Bugs me, too. I only use it when I absolutely have to. But it is free.