Invoice Software

I just got a macbook and now I need some software,
Hope this is the right spot I am new
I need a invoice program that is suited to construction. Billed mostly by the sq./ft. lin./ft.. I provide a service so I need to be able to turn the stock off so it does not show I am short 2000 sq.ft. of labour. I use Kbilling now and would like to keep all of their features plus more but stay mac compatible.
Thanks
Andrew

My business uses this service:

FreshBooks - Online Invoicing, Time Tracking and Expense Service

I work as a freelancer and I needed the online Invoicing tool to make the invoice process easy.
I have used almost all well knowned software but lately I have found the :
Billomat Online Invoicing Tool.

In my opinion is the best choise for every freelancer or a small company.