A free app for Android, by ClayFish Technologies.
This is an educational application for kids. It allows them to practice mental arithmetic, Vedic math, and abacus techniques. The app can be used for free. It is developed by a team of teachers and engineers. They have created this app with the students in mind.
How is it used?
The app generates mathematical problems and asks you to solve them. You can use the problems for practice or for learning. The app will allow you to select the level of difficulty.
It has three modes. You can choose one of them and solve as many problems as you want. You can also select the number of digits and the number of numbers. You can use both positive and negative numbers.