After Chris Grubbs and I finished up our work on phlombay.com for a class project about a year ago, we released what little code there was under the Affero Public License. My reasons were strictly idealogical, and I assume Chris wasn’t going to be selling proprietary versions of the site, so he went along just fine. However, since that time I’ve really wondered about the utility of license (as an aside, I’ve started work on phlombay again, but that’s another post entirely).
Unlike the GPL, the Affero stipulates that licensed software running on a network and providing a network or web service, must also provide the source. So while Google is not required to release any modifications to (the GPL licensed) MySQL backing up their search, they would be required to do so were the software licensed under Affero (I think…but what if the DB server is merely accessible via a webapp…hmmm).
Regardless, I had wondered about the utility of this license. However, that changed today after discovering some of the technorati services such as events and contacts. These services parse a page looking for microformats and then generate the appropriate file for that microformat (i.e. a vCard or iCal file). This is a perfect example of when code should be released under the Affero. By providing the code backing up these services, Technorati would enable users to setup their own servers (to relieve load, enforce uptime requirements, etc) while also ensuring that any modifications would be available to the public.
Though many object to the viral nature of licenses like the GPL, this objection is somewhat neutered in terms of webservices. Generally the service is available for (as in beer) already. Modifications to the code of this service probably serve no real monetary purposes; instead they improve the quality of the service. Therefore, there is less of a reason to shy away from a viral license when releasing code that backs webservices. Sure, in a perfect world we wouldn’t need viral licenses (or any licenses at all!), but that world is far off. Until then, the GPL and the Affero GPL are handy intellecutal property hacks.