Last week saw a quiet landmark in the history of the open source movement with the formal release of version two of the Mozilla Public License (MPLv2) and its approval as an official open source license. While to many it may look like just another legal detail, it is significant both for the way it was conducted and for the intent with which it has been created. This is a license aimed at unity.
Drafting and reviewing the license has been a very open process, for which Luis Villa deserves much credit. Conducted mostly on open forums, the discussion has led to many revisions of the text. Luis also approach the Open Source Initiative early, accepting input from the License Review group and obtaining the Board's approval easily.
Other coverage of the new license has focused on the modified patent-peace and other adjusted terms (goodbye, Netscape!) but the most important development in the creation of version 2 of the Mozilla license in my opinion is the inclusion of specific compatibility with the GNU General Public License (GPL). Previously, the Mozilla project used a complex and messy triple license arrangement to allow it to straddle the worlds of copyleft and non-copyleft licensing. Other users of the MPL (and its many vanity-named clones) tended not to bother, with the result that some code-bases were isolated from collaboration with the great universe of GPL-licensed software.
Using an approach pioneered in the European Commission's European Public License (EUPL), MPLv2 includes clauses that allow a project to optionally and explicitly declare compatibility with other licenses, most notably the GPL family. I believe MPLv2 is a significant upgrade on the previous v1.x family because of this explicit compatibility with GPL, providing for the first time a workable bridge between the permissive and copyleft paradigms. It satisfies the extremists of neither world, but pragmatically provides corporate-backed open source projects with a new approach. They can have a community that sustains permissively licensed code while also providing that community a way to relate to other communities with copyleft-licensed code.
With the steady decline of the dual-licensing business model (what some call "selling exceptions to copyleft"), it is becoming more and more apparent that permissive licensing is important to business contributors to open source. All the same, the GPL universe will not go away, so approaches that sustain the ideological gulf - including those that insist on eliminating all GPL code - are bad for everyone involved in business engagement with open source.
I welcome the MPLv2 as a positive contribution to unifying the common cause of many open source developers. Well done, Mozilla!