uMatrix is a free, open-source security and privacy application, designed to provide users with a comprehensive and powerful tool for managing their online security and privacy. It works by allowing users to create and customize matrix rules, which define which websites can connect to which other websites, and which requests and resources can be accessed from those websites. uMatrix also provides users with a range of additional security and privacy features, including the ability to block tracking cookies, scripts, plugins, and other types of code, as well as the ability to set permissions for specific websites or domains. Additionally, uMatrix can be used to detect and block malicious code or scripts, and to scan websites to ensure they are safe to visit.
Discontinued The project seems to be no longer developed. The latest version, v0.9.5.2, released in June 2015, can still be downloaded from the official website.