On the subject of licensing, I generally follow this imprecise flow:
Answer three questions:
A) Do you allow proprietary extensions to the project? In other words, consider this hypothetical example. 6502 GEOS sources are now commonly available online at Github. Further pretend that GEOS is still alive and well in the industry, and that you're a maintainer for the project. Suddenly, Joe wants to create a value-added distribution of GEOS using some proprietary code he's written, and works well for the C64/C128 versions of GEOS, but not for the Apple II version. If Joe would only release his extensions openly, others could (if they so desired) pick up the work of porting those extensions to the Apple II as well. Do you think it's OK for Joe to withhold his source listings and lock the license down?
YES or
NOB) Do you
allow (even if you don't recommend) contributors to select their own license terms for contributions which are
not to pre-existing files? Let's suppose Joe has a change of heart, and agrees to publish the sources to his contributions. Do you think Joe is free to change or replace a file with a given core project filename with his own? OR, do you feel that it's OK to use Joe's contributions even if he chose a different open-source license than you?
YES or
NOC) Do you want to apply these terms to the
project as a whole, or to
individual files comprising the project? If the former, answer
YES; otherwise
NO.
Then we arrive at the following truth-table.
Code:
A B C License
NO NO NO Apache V2.0
NO NO YES LGPL Version 2 or 3.
NO YES NO Apache V2.0
NO YES YES MPL Version 2.
YES NO NO Apache V2.0
YES NO YES Apache V2.0
YES YES NO Apache V2.0
YES YES YES Apache V2.0
As you can see, Apache is the most liberal of the licenses, being a BSD license derivative. However, MPL and LGPL are quite useful for providing legal guarantees about the openness of the project as well.
Note that I
did not list GPL license in this listing. While it has its place, the legal can of worms it opens up is, I think, too complicated for the majority of people who just want to window-shop for a license that best suits their needs. Not that GPL is inherently bad at its job; many great projects use it. However, know the terms you're agreeing to before selecting it. It's not a simple license, even if you can read it in one sitting.