Alfred + dc
I use Alfred 2 a lot on OS X in order to get things done. It doesn't completely change how I use the operating system, but it comes close. However, one of my pet peeves about it has always been that the built-in calculator is pretty terrible (even with the "advanced" equals-sign calculator). I realized this morning that I could fix this, and, lo, the dc alfred workflow was born.
It just takes its input and runs it through the
dc command-line utility, giving you a fully-programmable
RPN calculator. It's not quite as great as PCalc, but it's just a ^-space away. If you have Alfred,
you can just install the workflow and then use the script filter "dc" to run your math commands. Example: