There is a company I looked into called Virtuagym that offers nutrition and exercise software. It is a complete solution but the drawback I found was the high cost per month and a $500 fee. Oh and the fact that they also offer their program to the public for $6.95/month. Other than that it was very impressive.
I am using Trainerize now. It is a lot more affordable and has a nice calendar section to remind clients to work out.
Lisa is right that it does not have nutrition.
It is a little cumbersome to use and it takes a while to set it up but it is not a bad way to go. It can be very functional and you can customize it.