Types of open source licenses

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From Eric Steven Raymond’s “Varieties of Open-Source Licensing” (The Art of Unix Programming: 19 September 2003):

MIT or X Consortium License

The loosest kind of free-software license is one that grants unrestricted rights to copy, use, modify, and redistribute modified copies as long as a copy of the copyright and license terms is retained in all modified versions. But when you accept this license you do give up the right to sue the maintainers. …

BSD Classic License

The next least restrictive kind of license grants unrestricted rights to copy, use, modify, and redistribute modified copies as long as a copy of the copyright and license terms is retained in all modified versions, and an acknowledgment is made in advertising or documentation associated with the package. Grantee has to give up the right to sue the maintainers. … Note that in mid-1999 the Office of Technology Transfer of the University of California rescinded the advertising clause in the BSD license. …

Artistic License

The next most restrictive kind of license grants unrestricted rights to copy, use, and locally modify. It allows redistribution of modified binaries, but restricts redistribution of modified sources in ways intended to protect the interests of the authors and the free-software community. …

General Public License

The GNU General Public License (and its derivative, the Library or “Lesser” GPL) is the single most widely used free-software license. Like the Artistic License, it allows redistribution of modified sources provided the modified files bear “prominent notice”.

The GPL requires that any program containing parts that are under GPL be wholly GPLed. (The exact circumstances that trigger this requirement are not perfectly clear to everybody.)

These extra requirements actually make the GPL more restrictive than any of the other commonly used licenses. …

Mozilla Public License

The Mozilla Public License supports software that is open source, but may be linked with closed-source modules or extensions. It requires that the distributed software (“Covered Code”) remain open, but permits add-ons called through a defined API to remain closed. …