> is there a physic engine integrated?

Not yet. We had Chipmunk2D compiled in for awhile, but we haven't hooked it into Ruby yet.

> are the mobile targets going to be included or is it going to be a separate package?

We're trying to figure out how to package them appropriately, but at the moment we don't plan to sell this as a separate product.

>  what about services? like ads, gamecenter, steam, etc?

We aren't this far yet (and I will probably resist adding advertisements).

> Is there a plugin system in the plan to integrate those systems?

One of my great frustrations, as a Linux user, is watching cool Unity games get locked into Windows because they used a native plugin that blocked them from other platforms. I'm not saying we won't add something like this, but it makes me nervous.