Free/Libre Open Source Software

A Free Software source code license meets both open source and share alike constraints. Unlike generic open source, improvement without sharing is impossible. While share-alike such as Creative Commons allows restrictions on the sharing such as "no commercial use" or no derivative works, free software doesn't. In part this is because of the nature of software to be continually improved and the fact that it doesn't necessarily lose the powers or integrity that older versions have because new ones have been added. One can add functions to software that are invisible to users of the old functions, unlike for instance a book or a political platform.

The GPL and LGPL more or less completely define the free software movement. While there are other licenses, such as the peace license used by WarFTP in its early releases, these have not typically survived long.