These are really worthwhile apps. They are not drill and kill, but promote number sense, perseverence, and problem solving.
They are available
only for  iPads,  iPhones and iPod Touch and maybe some other Smart phones (depending on the app.) Some have a small cost, but most have a free app and then can then be upgraded for a cost.

Motion Math Fractions - on the number line

Motion Math Zoom - number line estimation

Motion Math Wings – multiplication

Motion Math Hungry Fish – addition and subtraction

Pearl Diver HD – fraction number line practice

Lobster Diver - same

Nine Gaps - great number sense

Chicken Math – find sums quickly before the fox eats the eggs

Operation Math Free - secret agent fun theme to get your child to practice math facts

Number League - super heroes catch the number villians- combine different numbers - $3.99

Kaakooma - Greg Tang - you can try it for free online. Suduko type sum game

Number Pyramid - number bond type practice for addition and subtraction

Jungle Coins - practice counting money

Jungle Time - practice telling time

Jungle Fractions - fraction practice

Candy Factory- fractions – this gets very difficult

Let's Tans – tangrams

Symmetry Shuffle -