From Apple App Store:
"With Numerosity, children will experiment with numbers and operations to develop their creativity with math. They'll move numbers around, dragging them into different positions to perform different operations so as to discover the rules of math on their own at their own pace."
From Wikipedia:
"Virtual manipulatives are a relatively new technology and are modeled after existing manipulatives such as base ten blocks, coins, blocks, tangrams, spinners, rulers, fraction bars, algebra tiles, geoboards, geometric plane, and solids figures.
Watch the video below for a good overview of the Virtual Manipulatives app:
http://www.youtube.com/watch?v=e6eBWcba7QQ