GCompris is an educational software suite with numerous activities for children aged 2 to 10. Some of the activities are game-orientated, but nonetheless still educational. These include computer discovery (keyboard, mouse, different mouse gestures), algebra (table memory, enumeration, double entry table, mirror image), science (the canal lock, the water cycle, the submarine, electric simulation), geography (place the country on the map), games (chess, memory, connect 4, oware, sudoku), reading practice, and others (learn to tell time, puzzles of famous paintings, vector drawing, cartoon making, etc.). It currently offers in excess of 100 activities, and more are being developed.
AbulEdu Calcul Mental is a software tool that trains children in mental calculation as stipulated by the French Ministry of Education for primary schools. Activities include addition, subtraction, multiplication of integers, addition tables (+2 to +9), times tables (x2 to x9), additional additives (to 10, to 100, to 1000), multiples (of 5, 10, 15, 20, 25 and 50), and orders of magnitude (with additions, subtractions, and multiplications). There is also an editor and selective launcher.
QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.