Go Concurrency Distilled publishes a free reference covering goroutines through scheduling and diagnostics with runnable examples

Sources: primary, discussion
Summary: Anton Zhiyanov's mini-book runs from goroutines, channels and select through pipelines, context, wait groups, data races, mutexes, semaphores, atomics, testing, scheduling and diagnostics, with each example editable and runnable in the page and a PDF alternative. It is written as a refresher rather than a first introduction, and it covers current API surface including WaitGroup.Go, context.WithCancelCause with context.Cause, and context.AfterFunc. It states the three error-handling shapes for concurrent pipelines side by side, and it includes the timer-reuse measurement that shows allocating one timer and resetting it in a loop rather than creating one per iteration.
Why it matters: It is free to read and tracks API added since most existing Go concurrency references, and the author states the book is AI-free.