A simple Touch Abacus aimed for the development of number sense in early math learning. The abacus has a long history in various cultures and is both concrete and abstract in some sense. This app provides the Chinese and Japanese versions. The Chinese abacus has seven beads on a vertical bar, while the Japanese version has five beads on a vertical bar. As a general rule, each bead in the lower deck represents one when moved toward to center beam. Each bead in the upper deck represents five when moved to the center beam. On the Japanese abacus, each bar could represent zero to nine units. By contrast, the Chinese abacus allows the representation of zero through 15 units on each bar, thus supporting calculation using the base-16 system. For the base-10 system, the two beads at the very top and bottom are not used. About the decimal point, users could, in fact, choose their own place, depending on their specific needs. This abacus app is developed by Dr. Lingguo Bu ([email protected]) using MIT AI 2, free for educators. Have fun playing with math.