Android developers interested in getting some spring in their step (get it?) might be interested in Rebound, a Java library that allows you to create animations of varying tension and friction that model spring dynamics. The usage is fairly simple, and the Rebound page includes an adjustable demo that shows off some of what the library can do.
It might take a bit of imagination to see uses beyond the demo, but there ought to be a lot of interesting approaches for anybody willing to get creative with it. According to Rebound's description:
The simplicity of Rebound makes it easy to integrate and use as a building block for creating more complex components like pagers, toggles, and scrollers.
So, anybody looking for some new ways to create animations or make a more interactive layout in Android ought to take a look. If nothing else, I'm ashamed to admit how entertained I was just playing with the demo.