"the Charm stuff" it is built on (and anyone else can use) is :)
And that's the stuff most of the industry (e.g. GitHub CLI) is using, btw.
Also, it looks like Crush has an irrevocable eventual fallback to MIT[1] allowing them to develop in open so you basically get all the bells and whistles available. We probably couldn't ask for more :)
[1] https://github.com/charmbracelet/crush/blob/317c5dbfafc0ebda...