Kalcul is an application which helps children at the age of 6 or above to improve their mental calculation skills. the children can choose between a practice mode in which it is given random mathematical exercises of a certain operation(+, -, x or /) and a level mode in which it has to solve existing levels which could have been created by a teacher or the parents using the built-in level editor.

http://edu.kde.org/kalcul/