Adds robust billing and invoicing functionality to your WordPress site. You can easily create, edit, and send customized and itemized invoices to your customers without leaving your WordPress control panel.
How it works: you create an invoice from your WordPress installation’s admin section, an email with a brief invoice description and a unique link is sent to your client. Your client follows the special link to your blog, where their invoice is automatically displayed for them. After reviewing the invoice, your client pays their bill using a credit card or PayPal account, and you are immediately notified.
Just add clients and let WordPress do the invoicing for you!