HexNumber This is a number converter. You can enter a decimal, hexdecimal, binary or octal number and see what it is in the other formats. The full version has a very much better interface plus you can convert to and from any base, it's available only for 0.5$
matrixmobile linear equations This app helps you solving systems of linear equations up to 9 unknown, working with matrices (inverse, transpose, multiply)
Maths Training Math Training is a fun way to practice your basic arithmetic. Choose from four signs of math!
MobileMaths Best Mathematical Tools and Scientific Applications for Your Mobile Phone