OpenLDAP is a user information server, Windows Active Directory is based on this protocol. Setting up when OpenLDAP correctly it can be used as a central authentication based of a network. meaning that your users can sign into any machine on the network with the same username/password.

Name: OpenLDAP
HomePage: http://lam.sourceforge.net/
Function: OpenLDAP is an open source implementation of the Lightweight Directory Access Protocol

Name: Squid
HomePage: http://www.squid-cache.org/
Function: proxy caching server for web clients

Name: SquidGuard
HomePage: http://www.squidguard.org/
Function: SquidGuard is a combined filter, redirector and access controller plugin for Squid