Slint has been around for quite a while now. A few years ago it was called SixtyFPS. I used it for a cross compiled Windows app (did 99% of the development on

Slint has been around for quite a while now. A few years ago it was called SixtyFPS. I used it for a cross compiled Windows app (did 99% of the development on macOS) and it was quite nice. It was a little limited as far as widget customization went (without getting down and writing your own widgets from scratch) but app ended up looking nice and behaving decently. It also lacked a few features I'd say were essential for any non-small desktop app (multiple top level windows weren't a thing a year ago, not sure if they've been added yet). I quite liked their DSL for the UI scripting. It was even typechecked a bit and interfaced with Rust in a fairly clean way. It's one of the nicer UI libraries I've used in a while.