Nuklear
A single-header ANSI C gui library.
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 renderbackend or OS window and input handling but instead provides a very modular library approach by using simple input state for input and draw commands describing primitive shapes as output. So instead of providing a layered library that tries to abstract over a number of platform and render backends it only focuses on the actual UI.