Programmer's Calculator Free
Programmer's Calculator Free is one of about a dozen similar apps in the Play store that do binary, octal, and hex conversions and calculations along with logical operations. It seems like a programmer's calculator is everyone's first Android app, and frankly none of them is especially compelling, but all of them do the job. On the other hand, when you need something like this, it's really handy to be able to do it on your tablet instead of trying to find the actual programmer's calculator you have lying around in a desk drawer, gathering dust.
The paid version of this app costs $1 and adds the ability to change themes.