I'm working on a framework inspired by React/Next.js which turns Haml into Ruby. It's 100% server side, but it runs pretty fast. I'm currently working on a rewrite, I just wish I had more time to work on it.
Both! I needed something like JSX, and I found Rux [1] but I had some issues with it, and then I found syntax_tree-haml [2] which gave me an AST that I could transform into Ruby. This is what the transformation looks like: https://gist.github.com/aalin/c0e4b0360a1f84d0283149fe4b2ce6...
I have always liked Haml because it's compact and easy to read.