Tokio

Official docs outline

Hello Tokio
Async main, the #[tokio::main] macro, the runtime, and writing a first async program.
Async in depth
How Rust futures, the Future trait, poll, wakers and executors actually work underneath async/await.
Spawning tasks
tokio::spawn, JoinHandle, the 'static and Send requirements, and how tasks are scheduled.
Shared state
Sharing data between tasks with Arc and Mutex, sharding locks, and avoiding holding a std Mutex across .await.
Channels
Message passing with mpsc, oneshot, broadcast and watch channels, and the actor-style pattern.
I/O
AsyncRead and AsyncWrite, copy, split, and reading and writing byte streams.
Framing
Buffered reads, parsing byte streams into frames, and write buffering.
Select
tokio::select! for waiting on multiple async operations, branch cancellation and cancel safety.
Streams
The Stream trait, StreamExt adaptors, iteration and mini-redis style subscriptions.
Graceful shutdown
Detecting shutdown signals, telling tasks to stop with CancellationToken or broadcast, and waiting for tasks to finish.
Bridging with sync code
Calling async code from blocking code and blocking code from async, spawn_blocking and runtime handles.
Unit testing
Testing async code with #[tokio::test], paused time, and mock I/O.
Getting started with tracing
Instrumenting async applications with the tracing crate for structured, span-based diagnostics.
Tokio API documentation
Crate-level reference for the runtime, task, sync, time, io, net and fs modules and feature flags.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.