Immediate-Mode-UI/Nuklear
This is a minimal-state, immediate-mode graphical user interface toolkit written in ANSI C and licensed under public domain. It was designed as a simple embeddable user interface for application and does not have any dependencies, a default render backend or OS window/input handling but instead provides a highly modular, library-based approach, with simple input state for input and draw commands describing primitive shapes as output.
https://github.com/Immediate-Mode-UI/Nuklear?utm_source=tldrnewsletter