Recently I came across Intuit’s Billing Manager. It is a VERY simple way to invoice your clients and keep track of payments. Did I mention it was free? It lets you send unlimited invoices to unlimited clients. Seriously, you can sign up and have an invoice sent out in less time than it will take to you to read this post.
Billing Manager lets you (for a fee) make use of Inuit’s Merchant service to accept credit cards, and you can even seamlessly upgrade to Quickbooks online. Pretty slick of them.
Seriously, if you need basic invoicing and payment tracking ability, you should check this out.