Billing Manager is an online application for small businesses to create invoices and track customer data. As a small business owner, this is a very valuable utility. Created by the same company that makes Quickbooks, Intuit has invested quite a bit of time into this program.

To make things practical, just the other day I was at a customer's house and used the program for the very first time. No more Paper Invoices with carbon copies, I was able to edit my customer's invoice, add files with a description of work done, and then send a copy of the invoice directly to her email to keep for her own records; how convenient!

Best of all it's free, to read why check out their reasoning.