So how did this little venture start? Well, when I first started contracting, I quickly found that I didn't have any way to estimate a decent rate, especially not while I was on the phone with an agency or employer. There are a number of 'rate calculators' on the web but most force you to go through a lengthy interview that isn't suitable for trying out "what if" scenarios. So I built myself a desktop application to do the calculations and then put it on the web for you to use
The plain fact is that there are as many ways of paying skilled contractors as there are companies who want to find you work, and each method--W2, 1099, Corp-to-corp--affects your compensation differently. Unfortunately, if you don't have a good idea of the value of benefits, employers and agencies will try to rip you off.
Moreover, there are a bunch of factors that go into calculating the correct rate: Your tax situation, the overhead of running your business. Skillserv's calculators allow you to plug in these numbers or, if you don't have a good idea of what the values should be, tries to pick reasonable values for you.