When doing business, there's enough software available you can use to conduct your business. If you have more than 20 clients, it is wise to think about professionalising your business software.
Typically you will need crm software that will interact with your timetracking and mail so you can manage your projects easy. Although cashboard doesn't offer all this functionality, if your business is as small as mine, it will do it's job fine : estimate, track and invoice your time.

Web site Cashboard helps you track your time, then facilitates the invoicing and payment process for your work.(Lifehacker)

There are several plans you can sign up with - and the first one is free. A magic word.