I'm a big fan of Aardappel, I used to co-run the Cube/Sauerbraten mapping website. I've never played with his language projects since they generally seemed too C-fixated to me... but despite that being the case here, I can at least see the value proposition clearly-enough that it seems really cool.

I think the README has been updated to be much more informative since it was first posted. tl;dr:

Stack-obsessed compiles-to-C programming language that promises to be faster than idiomatic C++ or Rust by using creative ideas about allocating dynamically-sized objects to the stack.