In this post I'll clarify some things regarding licensing.
First of all, there are two separate topics here: Licensing for the Intensity Engine and for Syntensity. The Intensity Engine is an open source project, while Syntensity is one particular project built using the Intensity Engine (that happens to be run by the same team).
Regarding the Intensity Engine, it uses the AGPL license. I recently elaborated a little more on the website about this, mainly that game content is not considered a derivative work. That is, if you write a game using the API, the game does not need to be AGPL licensed. It's yours and you can license it however you want. Only if you modify the engine itself, as opposed to creating a game using it, does the AGPL license become an issue. It's pretty much how Blender licensing works - make something with Blender and license it however you want; modify Blender itself, and you need to be GPL licensed.
Regarding Syntensity, my original idea was to require that all content be under a creative commons license or something similar, since I see Syntensity as closely related to the participatory culture movement (but in the context of gaming). By requiring such licensing, all the content on Syntensity would be free for use, in Syntensity and elsewhere. But it turned out that wasn't workable - not everyone is willing to use the same license (some artists insist on -NC licenses, for example). So by picking any one license, it would leave a lot of people out. And by picking several incompatible ones, there would be a lot of confusion. So in the end Syntensity will use the most minimalistic and generic licensing for user-created content: Whatever you create in Syntensity is yours, to do with as you want, but you grant everyone a license to use it freely within Syntensity. So how you let your content be used outside of Syntensity is entirely up to you (and you can completely disallow such use), while inside Syntensity we uphold the idea of everyone working together to create more and better games.
(If granting a license to people to use your content within Syntensity is a problem, then don't upload that content into Syntensity - use the Intensity Engine by yourself to run your content however you want, and with whatever license you want. It's open source, and that's what it's for.)