It uses its own unique language called Quby which is very similar to Ruby syntax.
There is good documentation available to get you started, but the forum is a little quiet with not much daily action.
Play My Code certainly has potential. However its main aim is to create an environment that is easy for people with little programming experience and I do not think Quby manages this. It would be very difficult for a beginner to sign up and get started.
The future does look bright though. The developers are still very active in the project and they are open to ideas. The next release is said to include touch support allowing for mobile game development – if this works well, it could be the spark needed to get Play My Code a community it needs.
I certainly would recommend taking a look at the site and what it has to offer. If they can get a community going it could take off. The promise of touch support is certainly exciting.