To build and to execute this system we use a lot of programs and services. A large number of that (but not all, see respective sites) are open-source
We use a lot of different software to list it completely but we like to say a specially "Thank you" to:
Sun Microsystems (now Oracle) for java, 99% of the project code is written in java.
Debian for a unique Operating System.
Apache Software Foundation for a lot of projects, in particular: Tomcat, httpd, james and commons.
Eclipse that permit to us to write the code.
Mozilla Foundation for FireFox, a unique tool for site building, with a "little" help from, Firebug and Web Developer extensions.
World Wide Web Consortium for documentation and validators.