DansGuardian

DansGuardian, written by SmoothWall Ltd and others, is content-control software: software designed to control which websites users can access. It also includes virus filtering and usage monitoring features. DansGuardian must be installed on a Unix or Linux computer, such as a server computer; its filtering extends to all computers in an organization, including Windows and Macintosh computers. DansGuardian is used by schools, businesses, value-added Internet service providers, and others.

As of now, DansGuardian is no longer maintained. Its successor is named "e2guardian". Provided by Wikipedia