A lot of Rust frameworks use sync io. The first generation does because the libraries for async didn't exist yet, and Rocket doesn't because (last I heard), the author said that he didn't feel the ergonomics were there yet, and that's one of Rocket's primary goals. So that leaves Actix, Gotham, and Shio, basically. Gotham hasn't been tuned for performance at all. I haven't seen any Shio benchmarks.

There are a lot though: https://github.com/flosse/rust-web-framework-comparison#serv...