It's similar. libdispatch is primarily a task queue to simplify and optimize multithreaded workloads in objc/swift. Tokio uses a similar task queue pattern for scheduling cpu-bound or blocking io, but the main feature is an non-blocking/asynchronous IO runtime. Overall, it's more similar to libuv (the async io library that powers node.js), but with built-in support for Rust's async/await syntax