CSS easing is great for ordinary transitions, but sometimes I want motion that responds like a spring: it can overshoot, settle, and feel connected to the distance it needs to travel. MotionSpring is a small JavaScript easing library and visualizer for exploring that behavior.
The visualizer makes the curve easier to tune before using it in an interface. It was a focused experiment in giving UI motion a more physical feel without bringing in a full animation framework. The library is published on npm.