How funny. I just spent the weekend AI slopping an FFI wrapper around notcurses because I couldn't find anything else. This looks amazing!
Since you asked for ideas in a different comment, here's something I put into my notcurses wrapper: grid and flex "css" layouts. Meaning the ability to say whatever.fixed(cols,...) and whatever.flex(:fr1) or whatever.grid(:fr1) and the ability to do a "grid-template-areas" style ascci art ala https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Grid...
Anything else meaning...? Ruby specific TUI library? I've been toying around with a lot of TUI's recently, landed on Textual (Python) for my most recent experiemnt, but Charm has been on my list to try out when I get a chance. There are also a number of other libs that will let you build quite robust applications in a number of languages (Rust, Python, Go, PHP, and those are just the one's I am aware of).
Indeed, looking for Ruby-specific stuff. There are a couple of ncurses wrappers that are not the friendliest things and at the other end of the spectrum there's the "TTY" code which, while nice isn't powerful enough to do what I was wanting to do.
Since you asked for ideas in a different comment, here's something I put into my notcurses wrapper: grid and flex "css" layouts. Meaning the ability to say whatever.fixed(cols,...) and whatever.flex(:fr1) or whatever.grid(:fr1) and the ability to do a "grid-template-areas" style ascci art ala https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Grid...