KoAbacusis an Android application developed by aboard. It is a free educational tool that aims to help users improve their mental arithmetic skills, specifically by using the Korean abacus. The Korean abacus is a calculating tool that has been used for centuries and is still widely used in Asia, Africa, and other parts of the world.

The app has a simple interface consisting of a Korean abacus with buttons for numbers, the four basic arithmetic operations, and other functions such as auto-test, speech, and sound. Users can test their skills by performing mental arithmetic operations on the abacus, and the app will provide the correct answer. The app also offers an auto-mental arithmetic function that can help users practice mental math automatically. Overall, KoAbacus is a helpful tool for anyone looking to improve their mental math skills.