software that is available under a license that grants the right to use, modify, and distribute the software, modified or not, to everyone free of charge.

This comparison only covers software licenses which have a linked Wikipedia article for details and which are approved by at least one of the following expert groups: the Free Software Foundation, the Open Source Initiative, the Debian Project and the Fedora Project.

The history of free and open-source software begins at the advent of computer software in the early half of the 20th century.

This article presents a timeline of events related to popular free/open-source software.