BlueBox Invoices for Mac

From Blue Box:

Blue Box Invoices was created to allow consultants, contractors, freelancers, and very small companies to quickly generate and track invoices and estimates. It is aimed at being a balance between "ease of use" and "general applicability" for all types of invoices.
Each invoice contains information about you or your company, information about the client, and specific billing information. Blue Box Invoices allows the generation of estimates or invoices, tracking of income related to specific companies or items, and tracking of full, partial, paid, unpaid, and overdue amounts. Invoices can be printed, faxed, or e-mailed. Blank invoices or estimates can be generated for use at the client site.