Free license is any license that guarantees the recipient of a work protected by copyright the freedom to use and enjoy the benefits of its use, copying and distributing, studying and modifying, and distributing modifications of that work. For these freedoms to be efficient, such licenses are irrevocably granted and, where applicable, require the work to be distributed in a manner that facilitates future modifications. In the case of software, it is necessary to always provide the source code.
Free Software Foundation Licenses
Some of the best known free licenses were created by the Free Software Foundation in the context of Free Software, specifically the GNU project.
In addition to offering freedoms, the Free Software Foundation licenses also implement the copyleft mechanism, which requires the preservation of freedoms in the distribution of copies and derivative works.
GNU General Public License
The General Public License (GPL) aims to guarantee four basic freedoms to the user of computer programs:
0. The freedom to run the program, for any purpose;
1. The freedom to study how the program works and adapt it to your needs. Access to source code is a prerequisite for this freedom;
2. The freedom to redistribute copies so that you can help your neighbor;
3. The freedom to improve the program, and release your improvements so that the entire community benefits from them. Access to source code is a prerequisite for this freedom.
GNU Free Documentation License
The Free Documentation License (GFDL), or GNU Free Documentation License, was originally conceived for technical manuals and for Free Software documentation, applying its principles to texts and other forms of expression. Its use has spread to other areas, for example, the GFDL was the license used in Wikipedia when it was created.
Creative Commons Licenses
Creative Commons is an organization dedicated to offering licenses less restrictive than all rights reserved for cultural, educational, artistic and non-software works. Some Creative Commons licenses are free licenses.
Some Creative Commons licenses are not free licenses, as they do not guarantee one or more freedoms. The following attributes that may be incorporated in choosing a Creative Commons license violate freedoms and may not be included in works designated as free.
Free licenses (Wikimedia Brasil)
Various Licenses and Comments about Them - GNU Project - Free Software Foundation
License information - Debian
Open Source Licenses
Licenses - Definition of Free Cultural Works
proposed Open Source Hardware (OSHW) Statement of Principles and Definition v1.0