Nand2Tetris was my favorite. I can't say the information (particularly the first half) has much practical application for me, but it was a lot of fun and deepened my understanding of what's going on at a low level. Homework is very well designed with a simulator you download to test your work on, then submit for automatic grading.
Udacity's Differential Equations course was pretty awesome too. I had taken Calculus previously, but I believe it's pretty approachable even if you haven't. The homework was very well designed, and involved fun problems like computing gravitational slingshots and curing diseases.
Coursera's "The Unwritten Constitution", also has a similar "The Written Constitution". Both are pretty awesome and really gives an in depth view of what the constitution is about (spoiler alert: it's about slavery), and even points out holes that haven't been challenged yet. Homework was writing essays and grading other people's, so not that well designed in that respect.
Coursera's "Coding the Matrix" is a Linear Algebra course. I took it the first time it was offered, and you pretty much had to buy the accompanying book to follow along. And the book unfortunately had a lot of "first version" issues. A lot of the homework wasn't explained very well, but it was all auto graded code. I think the issues with the book have been addressed with the second edition, not sure about the homework. I had already taken linear algebra before, so this was mostly a refresher, but even I found it hard to follow along in the last part, and never completed the last homework assignment.
On Youtube you can find "Fundamentals of Small Arms Weapons" from 1945. It shows how the action of a small arms rifle works. It starts as just a tube with a bullet, and works up to several different types of fully automatic actions. It's just a couple hours long.
Udacity's Differential Equations course was pretty awesome too. I had taken Calculus previously, but I believe it's pretty approachable even if you haven't. The homework was very well designed, and involved fun problems like computing gravitational slingshots and curing diseases.
Coursera's "The Unwritten Constitution", also has a similar "The Written Constitution". Both are pretty awesome and really gives an in depth view of what the constitution is about (spoiler alert: it's about slavery), and even points out holes that haven't been challenged yet. Homework was writing essays and grading other people's, so not that well designed in that respect.
Coursera's "Coding the Matrix" is a Linear Algebra course. I took it the first time it was offered, and you pretty much had to buy the accompanying book to follow along. And the book unfortunately had a lot of "first version" issues. A lot of the homework wasn't explained very well, but it was all auto graded code. I think the issues with the book have been addressed with the second edition, not sure about the homework. I had already taken linear algebra before, so this was mostly a refresher, but even I found it hard to follow along in the last part, and never completed the last homework assignment.
On Youtube you can find "Fundamentals of Small Arms Weapons" from 1945. It shows how the action of a small arms rifle works. It starts as just a tube with a bullet, and works up to several different types of fully automatic actions. It's just a couple hours long.