There are 3 repositories under single-header-file topic.
A simple-to-use modular, cross-platform graphics library. It combines the freedom of lower-level graphics libraries with modern C techniques, offering both simplicity and convenience.
An *single-header* alternative, pure C-focused wrapper to Apple's Cocoa API for OS X app development. Requires little to no Objective-C knowledge to use. Based on the original Silicon by EimaMei! Written in Pure C, no objective-c nonsense.