Sometimes is difficult to explain what playful design really is, because it could appear something like alchemy (and one of the goals of this space is to try to turn it in something more like chemistry, as Daniel Cook would say).
So it’s often better to come up with an example, which unvariably turns out to be Flickr.
One great example, though still a concept, is this work by Kaleidoscope, creators of The Greener Grass, a nice site trying to raise some ideas for a better future.
They have imagined a system to keep an eye to energy usage with an iPhone. And the interface they designed is a perfect example of playfulness (at least from a visual point of view). Check out, for example, this bit of interface:
which states the various points of energy usage in your home and reminds me of Metal Gear Solid‘s on screen map, which is one of the best interaction ideas of the game.
I would hav added just one thing: a community website where people could share ideas and maybe compete for a greener house. But that’s just the web part.
