Fibers are incredibly powerful, as they can be used to implement seamless go-like concurrency with async, colorless functions.
They were added to PHP by the maintainers of amphp (https://amphp.org), which is the best library for async PHP out there, providing a clean, object-oriented and async API for files, databases and everything that can make use of async I/O.
Async functions based on PHP fibers are explicitly uncolored, they do not require any special keywords to be invoked, and are explicitly swappable with any regular functions.
They were added to PHP by the maintainers of amphp (https://amphp.org), which is the best library for async PHP out there, providing a clean, object-oriented and async API for files, databases and everything that can make use of async I/O.