Ask HN: What's are good Rust projects to cut one's teeth on?

Ideally, a project that one can complete in a weekend. The ideal project doesn't need to be practical, but it should help solidify sub-topics in the language, such as lifetimes, elisions, generics, advanced type theory, and so on. Does anyone know of a repo of projects like that? Something more advanced than the Rust documentation, but builds up from fundamentals still.