3 blue 1 brown is a youtube channel that teaches math concepts. I've found it a much better introduction than other resources I've looked at. The Essence of Calculus series was particularly good.
But one issue is that, while the videos come with a few exercises sprinkled within (typically one per concept), they don't come with enough to really check whether I understand a thing.
Last year I tried binging the channel but kept running into issues where I'd want to do additional practice, so I'd try Khan Academy or Brilliant.org. But it felt like the exercises were introducing concepts in a fairly different order, or without using the same metaphors/explanations/keywords that 3-blue-1-brown was. So it was hard to tell what exercises corresponded with what. (Brilliant.org was better overall than Khan Academy but still felt like a completely different lesson plan, with somewhat less-good-explanations)
Eventually, bouncing between brilliant.org and 3 blue 1 brown resulted in me running out of steam and giving up.
I've emailed the creator about it but even if they were excited about it I imagine it'd be quite a while before anything useful came of it.
I'd be generally interested in a project of crowdsourcing exercises that correspond to individual 3-blue-1-brown videos. Since I'm currently trying to re-ignite my interest in the Linear Algebra series I thought I'd ask specifically about that, although if people happen to have cached thoughts about other series that'd be cool.