TypeScript Coach (https://ts.coach)
While I love the official TypeScript handbook, it's not easy to play around with the code examples or approach it as a beginner. I started working on a complete TypeScript tutorial that also showcases some advanced use cases. All the code examples run in the browser, and there are some neat visualizations that clearly show what the type system has picked up.
I've been trying to fix some of the performance issues, finish writing all the content, and adding documentation before making the GitHub repository public - right now the page can hang when loading a long tutorial.