Copyright and copyleft

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What we call copyright is a set of laws meant to protect the rights of content creators and publishers.

The open source movement

the copyright symbol
the copyleft symbol


“Free as in Freedom, not free as in free beer”
- Richard Stallman

Copyleft is the mantra of the open source movement

  • not a legal term
  • simply a play on words
    • copyleft is the opposite of copyright
  • copyright is designed to prevent people from stealing each others ideas
  • copyleft is the mantra that ideas are meant to be stolen
  • this vision is often realized by using the GNU General Public License to copyright software

There are many so-called open source movements which focus more on free beer than on freedom.


The GNU Project is a collaborative group founded by Richard Stallman

  • whose goal is to foster the spread of freedom (as differentiated from free in terms of price)
  • began by developing the GNU free operating system, a clone of UNIX
  • GNU is a recursive acronym for “GNU’s Not Unix”
  • wrote the GNU General Public License, which has inspired a generation of open source developers to release projects under this or similar licenses

The concept of copyleft was described in Richard Stallman's GNU Manifesto in 1985, where he wrote:

GNU is not in the public domain. Everyone will be permitted to modify and redistribute GNU, but no distributor will be allowed to restrict its further redistribution. That is to say, proprietary modifications will not be allowed. I want to make sure that all versions of GNU remain free.

GNU General Public License

the GNU logo
  • a legal licensing contract, written by Richard Stallman
  • adopted by many open-source software makers
  • allows anyone to modify the software any way they want
    • so long as the derivative software is non-commercial
  • guarantees that derivative works will always remain free
  • GNU Lesser General Public License
    • a slightly more lenient version of the GNU General Public License
    • allows some commercial software to use the copyrighted work, so long as those programs are not derived from the work

There are now many spin-off licenses that maintain the basic ideas in the GNU General or Lesser Public Licenses, but differ in some details.

Popular open source projects

Operating systems:


Product design:


  • Bitcoin, a decentralized crypto-currency.

Decentralized applications:


Web publishing:

  • MediaWiki wiki platform that powers sites like Wikipedia (and this site)
  • WordPress web publishing software

Media playing:

  • VLC media player


Web browsing:

Science and Engineering:

  • SciPy, an open source collection of tools in Python to assist math, science, and engineering
  • OpenEEG electroencephalogram brain imaging hardware


... and many others ...

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