David Simmons dives deep into [tokio-core](https://crates.io/crates/tokio-core), [futures](https://crates.io/crates/futures) and asynchronous programming in Rust in general.
This article helped me quite a bit to understand how all the different things work together.
It's the missing documentation for the named crates and combines a look into the code, a look at the executed syscalls, pretty diagrams and a lot of text to explain everything in detail.
(I had this saved for a while, but never managed to read it)