Today I released v1.0.0 of Usagi Engine after making a bunch of small games, getting feedback from developers, and stabilizing the API. It's simple, has a great developer experience (CLI-based, init template, Lua plugin integration, and cross-platform export for web, Linux, macOS, and Windows with a single command).
The engine is public domain, and its source is on GitHub (linked from the website).
Rust was a great fit for this project due to its stability and tooling. The crate ecosystem is a real highlight for me. Plus clippy. I made a couple of games in Rust in the past (using Macroquad) which prepared me for this project. But for Usagi I decided to go with Raylib for it's maturity. Usagi is using sola-raylib, the Rust bindings for C Raylib with some Rust-y wrappings. I maintain these bindings, which also was a big help to be familiar with what's possible with Raylib.
The well known tools that are similar are Pico-8, Picotron, Love2D, and DragonRuby Game Toolkit. They all have their strengths and weaknesses. I think Usagi fits in a little spot amongst them where it's free, open source, and has a much more modern developer experience.
Now that the engine is v1.0.0, I'm going to focus my energy on making games with it, writing a book of tutorials, and creating video screencasts. I love sharing what I learn and helping people make their games.
I'd love it if you checked the engine out, and I'm looking forward to seeing what people make.