Businesses wishing to avoid using the GPL tended to follow the example of the Mozilla project and created their own license. As a result, over 60 new licenses were approved by OSI in the first few years of the open source era. But this proliferation has come with a cost. Open source licenses often don't mix; when you make your own, you condemn your project to isolation. Creating a new license like this is a problem that arises from a fundamental misunderstanding of the role of the license in open source, treating it as a traditional bilateral legal agreement. Instead, an open source license is a multilateral agreement, "the constitution for the community," as Eben Moglen once put it.
In recent years, new projects have been much more aware of the role of the license in enabling community formation and function. The result has been a trend toward liberal licenses such as the Apache License or the BSD/MIT licenses, thereby eliminating perceived barriers to participation for corporate contributors. OpenStack, for example, uses liberal licensing.
Yet even projects that use the liberal BSD Unix license have at times railed against corporations who use their work without contribution, suggesting there's a role for copyleft, too. Most communities are offended when a profitable consumer of their work is all take and no give. This sense of justice will likely push the needle that has swung full-scale from GPL to BSD back to the middle ground, best represented by the recently revised Mozilla Public License, MPLv2.
MPLv2 is explicitly compatible with the GPL, and it contains no clauses that prevent mingling with liberal licenses, aligning it with the sensibilities of most of today's open source communities. It does include a weak copyleft requirement that changes to files managed by the project must be published, but it allows developers complete freedom to use the compiled binaries any way they want, including mixing them with non-open-source code to create proprietary products.
3. The specter of software patentsThe legal system is having an increasing effect on today's open source movement in the form of software patents, a stark contrast from 15 years ago.
A form of social contract between inventors and society, patents exchange a temporary monopoly of a practical invention for the publication of that invention so that the public at large -- "the commons" -- can benefit from it.