WebGL Studio
This is amazing and feels very fluid. I think it is part of a web-based software trend that will surprise a lot of people who think of the web at best as an interactive document display system. Another app that has a very snappy UI like this is <a href="http://OnShape.com" rel="nofollow">http://OnShape.com</a> CAD software, which is full featured 3D solid modeling without any plugins (all JS and WebGL).