Arithmethon makes educational software for Windows and Android.
The Arithmethon app is a cross-platform mental arithmetic and mathematics exercise program that seeks to apply real-world experience of the process of learning maths and arithmetic.
Use it once or twice a day, and your (or your child's) arithmetic will improve noticeably.
Arithmethon has exercises for addition, subtraction, multiplication, division, squares, square roots, word problems and more.