ZAP (Zed Attack Proxy) is a free and open-source web application penetration testing tool developed by the OWASP Foundation to help find vulnerabilities in web applications. It includes features like an intercepting proxy, scanners, a spider, fuzzing tools and a macro language to aid in testing applications. The tool is actively developed by a community of contributors and used by both professionals and beginners for tasks like security testing, debugging and regression testing of applications.