I've made a repository for a very simple C OpenGL renderer API.
It looks this simple to use:

Render_Begin_Frame(&renderer);
Render_Push_Quad_T(&renderer, rect_init(400, 400, 100, 100), Color_Magenta, white_texture);
Render_Push_String(&renderer, &inconsolata_font, str_lit("Text Rendering!"), vec2_init(500, 100), Color_Yellow);
Render_End_Frame(&renderer);

It fits in precisely 300 Lines of code, and is super easy to extend
https://github.com/PixelRifts/easy-renderer
For a nice demo: I made a little tetris clone... so enjoy my terrible gameplay 😛