One thing we pondered might be cool for the future is some kind of iframe-sandboxed JavaScript to add object functionality, but already you can add to the functionality using behavior scripts called Interactings. http://manyland.com/info-interacting This is the way you can currently extend the logic, and we're setting most of our Interactings for tutorial purposes and such to 'clonable', meaning you can collect the object and adjust and copy its graphic & code. Take a look at some of the videos on the Interacting help page to get an idea, and please contact us if you have any questions or suggestions!

It's also not closed in the sense that you cannot hack the hell out of it once you buy a license. The closed part is just so that Dom gets his 99$ license fees (IMO a steal).