Typst is available as a standalone compiler

With realtime results?

yes, it does and its realtime. personally, I use typst locally, but the online editor utilises WASM, so if I'm not mistaken, the rendering is real-time and handled by the front-end.

You are talking about incremental compilation?

no, I pointed towards the joy of writing in a proper IDE. but to your point: overleaf is a key enabler of latex and its cool to see typst offers a similar route