Understanding Open Source and Free Software Licensing

Application and Philosophy

All of these licenses have been used in practice, both in licensing software maintained in the open source community and in providing the basis for commercial applications of programs derived from open source models. The BSD, MIT, and Apache Licenses, longer established and more frequently adopted than the Academic Free License, provide the examples described in this section.

Each of these three licenses has contributed to the widespread commercial adoption of the programs they license, frequently (though not always) through incorporation into products distributed under a proprietary license. This is completely consistent with the language and intent of the licenses. This also reflects their place of origin. For example, both Berkeley Unix and the X Window System were research projects; the goal of their creators was to explore technology, to provide a proof-of-concept implementation, and then to permit others to build on that work. Commercial applications readily followed successful implementations of research ideas.

BSD Unix became the basis for commercial versions of Unix ranging from Sun's Solaris to Apple's Mac OS X. BSD-derived proprietary versions of Unix outstripped the commercially licensed AT&T versions relatively quickly, and they dominated the commercial Unix market until the 1990s when Unix was challenged by GPL-licensed Linux distribution. The TCP/IP software stack that was part of the Berkeley networking release became the basis for almost ...