Relatively low-poly skyline silhouette to help fill in middle/background areas of a scene, especially for ones made in [Spoke](http://hubs.mozilla.com/spoke).
It's meant to act almost like a skybox/skydome but because it's made only with geometry and no textures/alpha transparency, it should be good for lower-end devices.
If you use a couple of them and scale/rotate them, you could create a decent parallax effect.