InvoiceThat.com is a super simple way to invoice your clients. In about a minute, you can sign up and start using this service for free. Paid subscriptions are also offered on a monthly basis with a 30-day free trial. There are no contracts and you can cancel at anytime. Major features include: managing client contact information, painlessly generate invoices, quickly email invoices to your clients, setup billing rates to eliminate unnecessary typing, download invoices in PDF format (for Brisk and Jammin accounts), and get paid using your PayPal account (for Jammin accounts only).