The async-listener project is a polyfill that provides the `process.addAsyncListener` API for Node.js versions prior to when it is natively supported, allowing developers to add behavior to async calls. It's designed for Node.js developers who need to track or modify asynchronous operations, such as debugging or monitoring tools, in older Node.js environments. The project is based on Trevor Norris's implementation and includes features like callbacks for before/after async execution and error handling.