kino

A high-performance Ractor web server for Ruby 4.0+: Rack 3-based, with a Rust Tokio/Hyper front-end and Ractor-parallel Ruby workers and threaded fallback mode. Maintained by yaroslav on GitHub, where it has earned 173 stars from the community.

It's actively developed around concurrency, http-server, parallelism, and is a solid reference for anyone building with these tools.