FullCalendar is a highly flexible and feature-rich JavaScript library designed to create customizable calendars on web applications. It provides a comprehensive suite of tools for rendering interactive and responsive calendar views and supports scheduling and event management functionalities. Users can choose from various display options, such as month, week, and day views, and can integrate the library with popular frameworks like React, Angular, and Vue. FullCalendar is also equipped to handle drag-and-drop event functionality, time zones, and recurring events. The library is widely used for its versatility and ease of integration into existing web projects.