I've been working on my own programming language, Haven - https://github.com/miselin/haven

Lately, I've been hacking on improving its linear algebra support (as that's one of the key focuses I want - native matrix/vector types and easy math with them), which has also helped flush out a bunch of codegen bugs. When that gets tedious, I've also been working on general syntax ergonomics and fixing correctness bugs, with a view to self-hosting in the future.