Free software licenses (Copyleft, GPL, LGPL, BSD, Apache, MIT/X11, …)

  • GPL/GPL@wiki is one of many free software licenses. It covers derivative work with a Copyleft and not end-user licensing (for now), so it doesn’t cover for example the use of GCC compiler to compile your close-source product.
    • Your product must also be GPL if change or include GPL source code (no need to ask for permissions) or if link statically (or also dynamically according to FSF interpretation).
    • GPLv2 vs GPLv3: addresses patents, license compatibility, DRM, and “Tivo-ization” hardware.
  • LGPL – Lesser GPL relaxes and allows free libraries to be used (linked statically or dinamically) and distributed with proprietary software. For example, GNU Libc used by Linux is LGPL, otherwise closed-source products couldn’t legally run under Linux.

  • AGPL – Affero General Public License is GPL plus addicional section to trigger copyleft to application service providers. It requires that the complete source code be made available to any network user of the AGPL-licensed work, typically a Web application.

  • BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the redistribution of covered software. The revised/modivied 3-clauses license allows unlimited redistribution for any purpose as long as its copyright notices and the license’s disclaimers of warranty are maintained. The license also contains a clause restricting use of the names of contributors for endorsement of a derived work without specific permission. Apache 2.0 license is better for substantial programs, since it prevents patent treachery.

  • MIT/X11 license is permissive license, very similar to 3-causes “modified” BSD license, except that the BSD license contains a notice prohibiting the use of the name of the copyright holder in promotion.

  • Apache License is permissive in that it does not require a derivative work of the software, or modifications to the original, to be distributed using the same license. It still 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 (excluding notices that do not pertain to any part of the derivative works); and, in every licensed file changed, a notification must be added stating that changes have been made to that file.

  • MPL – Mozilla Public License partial copyleft, hybridization of the modified BSD license and GNU General Public License (GPL) that seeks to balance the concerns of proprietary and open source developers. The MPL allows covered source code to be mixed with other files under a different, even proprietary license.

See choosing an OSS license and comparison of free and open-source software licenses.

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