RESTEasy is an open-source framework for building RESTful web services and Java applications. It is a part of the JBoss Enterprise Application Platform and provides features like client and server-side annotation support, HTTP method and parameter support, content negotiation, and exception handling. RESTEasy simplifies the development of RESTful services and offers several extensions and integrations with other frameworks and technologies. It is widely used in enterprise web applications and offers easy integration with other JBoss technologies.