https://github.com/yaroslav/kino

Rubyists who experiment with Ractors, put them to work! Meet Kino, an experimental performant Rust/Ruby Ractor web server (with a threading fallback).
Note that Ractors are officially experimental in Ruby 4.0, and so is this server. Rails cannot run on Ractors yet, but it will, sometime in the future.

Performance: when your app IS fully Ractor-shareable, on AWS (Ruby 4.0 + YJIT) vs a Puma fork cluster:
• ~15× less RAM — 80 MB vs 1,256 MB
• +32% on pure CPU
• 1.5–2× on I/O-light routes
Raw runs + methodology in the repo.

Kino also ships kino --check to find Ractor incompatibilities for you.