The Tokio async stack for Rust (https://tokio.rs).
They did a really nice job of building thin layers up the stack from byte buffers (bytes), to async-friendly logging (tracing), basic IO (mio), async runtime (tokio), generic request/response services (tower), HTTP (hyper), and a web framework (axum).
Each of the layers are useful independent of the other layers above, and every one is has a thoughtfully designed, pragmatic interface.