am not a lawyer, so all disclaimers apply

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basically different projects have different criteria:
a. drupal needs all modules as GPL if they are part of Drupal CVS. I suspect like Joomla, Drupal will make it a requirement that ALL modules have to be GPL sometime soon. This
b. CiviCRM needs code to be licensed using AFL if it will be part of CiviCRM. We've blogged about this in the past as to the reasons why etc. If you need very specific legal answers, you might need to chat with our lawyer (Larry Rosen from rosenlaw)
c. CiviCRM uses AGPL since we do like the network effects of AGPL (compared to GPL). Some members of our team are much stronger GPL advocates than others. I don't think there are lots of cases where folks have not used us because of the license (only one case that i know of).
d. Ultimately, you should choose a license that you are comfortable with and meets the needs of your users. You should definitely go with an OSI approved license, rather than making your own. To a large extent, licensing discussions are similar to talk about religion. Everyone feels that their chosen license is superior

lobo