AmplifyJS is a JavaScript component library produced by Spritle Software that provides tools for common web application problems. It includes APIs for making AJAX requests, client-side component communication, browser storage, and publishing/subscribing to messages. The request API provides a way to define, request, cache, and handle responses for API calls. The store API provides a consistent way to store and retrieve data in client-side storage. The pub/sub API facilitates publishing messages that components can subscribe to.