[1] For more information about the philosophical background for open-source software, see free software movement and Open Source Initiative.
However, nearly all software meeting the Free Software Definition also meets the Open Source Definition and vice versa.
A small fraction of the software that meets either definition is listed here.
Some of the open-source applications are also the basis of commercial products, shown in the List of commercial open-source applications and services.
Be advised that available distributions of these systems can contain, or offer to build and install, added software that is neither free software nor open-source.