I dunno why, because I'm certain I've seen games like this somewhere, but this just seems really cool and sorta inspiring, along the lines of "hey, you can just write code and toss it in a browser and go". (Not to be rude; I'm sure it took a lot of effort.) This is one of the first times I've ever felt this way. Ever since '95, I've never been impressed with a web version of something, because usually it's a weak imitation of a native program. But this just feels like something different.
JavaScript/ html5 has pros and cons but one thing that is fun is to be able to quickly release updates, sometimes several times over the course of a day, which will then instantly be visible to everyone in the world (and since we're using a browser wrapper for e.g. the iPad version, it will also be updated across devices).
Is this an open-source project?
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).