How to choose an open source license for an app

it's simply a matter of you to decide how your product should be used and how much control over it you want in the future.

up until recently, I published all my code under GPL. One recent project was to develop an interface library which is supposed to work with proprietary modules, so I used the MIT license: http://search.cpan.org/dist/SIAM/

the rule of thumb is quite simple: if you're in a project where your work is intended for a mixed enterprise environment, with parts of non-opensource code integrated with your work, then choose MIT or Apache license.

Otherwise, GPL works fine for most cases.

for example, an open-source library which is intended to be extended by enterprise-specific drivers, is better to be published under MIT than GPL