Auditorium:

I spent a bit of time playing this today: Auditorium. It's very satisfying, I think. I wish I had more details about it, but there isn't much on the website except the demo, which I recommend you go and try out for yourself. Thanks to Think or Thwim for finding it.

Update:
Ars Technica has picked up on this, and they've provided some details in their article.