Free and open source software licenses

This is a description of most commonly used free software licenses. The licenses are approved by atleast one expert group at the FSF, the OSI, the Debian project, or the Fedora project.

Basic License Structures

  1. Open-source license is a type of license for computer software and other products that allows the source code, blueprint or design to be used, modified and/or shared under defined terms and conditions.[1] This allows end users to review and modify the source code, blueprint or design for their own customization, curiosity or troubleshooting needs.
  2. Free Software - provides freedoms to use, study, share (copy), and modify the software. Open-source license criteria focuses on the availability of the source code and the ability to modify and share it, while free software licenses focuses on the user's freedom to use the program, to modify it, and to share it.[2]
  3. Attribution (BY) - Licensees may copy, distribute, display and perform the work and make derivative works based on it only if they give the author or licensor the credits in the manner specified by these.
    1. 'Advertising clause' in some licenses required all advertising of the software and its derivatives to display a notice crediting its authors. This was a stricter clause resulting in failure to link from code with a different license. This clause is now rare in modern licenses, which only require attribution in documentation.
  4. Share-alike (SA) or Copyleft: Licensees may distribute derivative works only under a license identical to the license that governs the original work.
  5. CopyFree: Freedom to distribute modifications
  6. Non-commercial (NC) clause - Licensees may copy, distribute, display, and perform the work and make derivative works based on it only for noncommercial purposes. Licenses that do not put this restriction are available for commercial use.

Approved License Forms

  1. Open Source Initiative (OSI) approved licenses based on Open Source Definition (OSD) must be open-source software, and eligible for commercial use.
  2. Permissive free software license is a Free software, with no added restrictions other than Attribution. e.g. MIT License and the BSD licenses.
  3. Free software foundation recommends software to be Free, and copylefted to ensure Freedoms are propagated to modifications. e.g. GPL license

List of Licenses

Below is a list of licenses that are popular and widely used or with strong communities [3]

  1. GNU GPL - GNU public license is a Free/Open-source software license, with pure copylefted license promoted by FSF. GPLv2 also made it patentLefted, so that if it can't be used freely legally by all, it can't use GPLv2 and hence can't be distributed at all. GPLv3 furthered it by enforcing strong leaving of legal rights to users. GPLv3 is not compatible with GPLv2 code, unless latter was licensed under GPL v2 or later.
  2. LGPL - does not guarantee the end user's complete freedom in the use of software: it only guarantees the freedom of modification for the LGPL-parts, but not for any proprietary software-parts. There by it allows derivative usage in GPL code, as well as linking with non-GPL and proprietary code.
  3. BSD licenses - class of Permissive free software license. Original 4-clause BSD License required attribution in advertising material which restricted compatibility with code from other licenses. NewBSD 3-clause license removed such restriction, and is fully compatible with GNU GPL. Later, Simplified/FreeBSD License removed even the non-endorsement clause.
  4. MIT license/Free BSD license/ISC license - free permissive licenses, functionally equivalent to each other. BSD, MIT, ISC licenses do not include an express patent license.
  5. Apache license - limited CopyLeft. Generally permissive, but requires application of the same license to all unmodified parts and, in every licensed file, any original copyright, patent, trademark, and attribution notices in redistributed code must be preserved; and, in every licensed file changed, a notification must be added stating that changes have been made to that file. ALv1 had advertising clause in attribution, which was killed in ALv1.1. ALv2 allowed license to be included by reference instead of each file, and requiring patent license on contributions, making it compatible with GPLv3.
  6. Mozilla Public License - limited CopyLeft. Each file is copyleft, but entire program is not. So modifications to existing files need to be re-released under MPL while newer files can be closed sourced. Sun's Common Development and Distribution License is based on Mozilla Public License.
  7. Eclipse Public License - business-friendly free software license and features weaker copyleft provisions than GPL, enabling linking with other codes. It however requires contributors to grant patents to all recipients. IBM's Common Public License had strong similarities to EPL, and been deprecated in favor of EPL to reduce license proliferation.

Redundant Licenses

Licenses that are redundant with more popular licenses

  1. Academic Free License (redundant with Apache 2.0)
  2. Attribution Assurance Licenses (redundant with BSD)
  3. CUA Office Public License (redundant with MPL 1.1)
  4. Eiffel Forum License V2.0 (redundant with BSD)
  5. Fair License (redundant with BSD)
  6. Historical Permission Notice and Disclaimer (redundant with BSD)
  7. Lucent Public License Version 1.02 (redundant with CPL)
  8. University of Illinois/NCSA Open Source License (redundant with BSD)
  9. X.Net License (redundant with MIT)

See also

References