MicroUI – A tiny, portable, immediate-mode UI library written in ANSI C (opens in new tab)

"Accessibility" is an open-ended set of functionality, not a checkbox; it is never "complete", there is always room for improvement. Colorblind support (which ones)? High-Contrast mode? Adjustable text size? Screenreader integration? Localization? IME support? Keyboard navigation? Keyboard remapping? Functional entirely without a keyboard? Touch support? Pen support? Dyslexia-aiding typefaces? The list goes on and on.