This is a game engine that I'm currently working on. It has a C "core" and a Lua scripting interface. The C core defines syntaxes for all the essential data types necessary to make games (menus, actors, fonts), and these data types have scripting slots in which you can install Lua code to configure their behavior and make your own games.

As an example, this is you define a font in my engine: https://monospace.games/engine/manual/font-object-examples

The engine tries to make it as easy as possible to create new games and modify existing games by not obscuring its assets (see the basics section of the manual for more info), and my hope is to enable an ecosystem of indie creators with it. It still has a long way to go though, for example GUI related parts (menus, widgets, canvases, text buffers) have fairly matured, but game world related parts (maps, actors) are still heavily in development.

My main inspiration in the development of this has been Emacs (although I shied away from using Lisp for scripting), and the project has experienced a lot of convergent evolution that made it resemble web browsers. For example menu styles are "cascaded" similar to CSS, even though I wasn't familiar with web development at all when I first started this project.