Not software, no. Hardware. An actual device, roughly the size of a mouse or a small point-and-shoot camera, which plugs in to your computer and takes readings from your screen.
Have you read this page?
I really like Frontier Digital. Some reviews here.
Lots of people talk about RGB Digital, but I found their quality a bit disappointing, to be honest.
However, I strongly recommend you get test prints from both places, and make your own decision. Remember that you need to do that BEFORE you calibrate your screen. You can't calibrate until you have pro lab prints in your hand.