This simple Javascript program shows 8-bit values in decimal, hexadecimal, binary, and ASCII. You can type a value in any of the windows, and when you push return/enter, it will be displayed in all the windows. You can also increment and decrement the displayed value.

The values are limited to 8 bits; if you enter a larger value, the overflow will be silently be discarded.

View the source to see how it works.