Open Source-How Computers Really Work!
Welcome to a site completely dedicated to open source. One would have to assume since you are visiting this site, that you already understand the open source philosophy. One of the big projects of open source is Linux. Linux is an operating system, similar to MS DOS/Windows. It is completely available in both source and binary format. Some distributions of Linux are free(as in free lunch) to download, where others ask that you pay for them. When paying for a Linux Distribution, you are primarily purchasing either support, or a proprietary product bundled with the distribution.
Many people feel that Linux should be called GNU/Linux, due to the fact that Linux is only a kernel. Most of the other tools used in the Linux environment were developed and are maintained by the GNU foundation. GNOME is one example. GNOME is a Desktop Environment, similar to Windows. It is maintained by the GNOME foundation, an offshoot of GNU.
Linux isn't the only open source project however, Mozilla Firefox also is open source. Firefox is released under a different license than Linux is however. Linux is released under the Gnu General Public License, and is produced by Open Source Development Labs(OSDL). Firefox is released under the Mozilla Public License, and is produced by Mozilla Foundation.