Calc X is a free and easy to use, small, simple calculator that has the following modes: Decimal, Hexadecimal, Octal, and Binary.
When switching from mode to mode, some keys on the keypad will change to reflect the mode you`re in.
For example, when switching from decimal to hexadecimal, the sin, cos, and tan keys will change to A, B, and C for hex input. Then, if you change to binary mode, the keys will change to XOR, AND, and OR.