5.1.6. Licensing Models

• GPL and LGPL
  • GPL guarantees the following freedoms (as in free speech, not free beer)
    1. You can run the program as you wish for any purpose
    2. You can study the source code and change it to do what you want
    3. You can make copies and distribute them
    4. You can distribute modified versions
  • Derivative work inherits license (mistermed virus nature of GPL)
  • Linking is considered derivative work in GPL but not in Lesser GNU Public License (LGPL)
    -> GNU libc is most prominent LGPLd program

• BSD style licences:
  • MIT: Copyright and permission notice must be included in all copies or substantial parts of the Software
  • BSD: non attribution provision (contributers names may not be used to endorse or
    promote products without permission), advertising clause (removed 1999)
  • Apache Free License v2: strong branding, contributions become part of licensed work, license terminates if licensee initiates patent litigation
  • -> BSD style licenses have no such derivative work clause and thus cannot prevent "misuse" of software (OpenBSD, FreeBSD, NetBSD)
  • -> commercial application is usually intended (BSD Unix, X Window System)

• MPL (Mozilla Public License)
  • somewhere in between BSD and GPL
  • weak Copyleft: MPL source code modified stays MPL, but can be combined with any other code to form a proprietary program
  • NPL (Netscape Public License): variant that gives original developer the right to distribute
    modifications by other contributers under whatever terms it desires.

• Open Source vs. Free Software

• Open source can be any license acknowledged by the Open Source Initiative (incl. all mentioned above)

• Because of so many licenses all dubbed "open source", check which freedoms they really entail