There are many web utilities that offers you invoice services, invoice is really very important if your are running a freelancing website. If you want to do it free then do it on WordPress, there are many free plugin already available in WordPress plugin repository that allows you to manage invoice and billing in your WordPress based website.
Using CashPress you can easily manage all your documents online. It allows you to create secure invoices and keeps estimates of your clients. You can deal sealing presentations, managing document libraries, creating new clients database. View more of its screenshots here.
Easy and flexible invoicing system for WordPress, it can get easily integrated with your Paypal account. It has been loaded with very few features including a little bit for your business, notification email subject customisation, and PayPal information, it makes it easy, fast and easy to setup.It only supports PayPal manual payments. Following screenshot shows invoice page which comes visible for clients. It has simple options for paying invoice and viewing previous transactions.View more of its screenshots here.
This is a Project Management solution for WordPress users. You can select a front-page where your clients can authenticate and view summaries of their information, invoices and projects. They can add new tasks which then get added to dashboard for moderation. Its a BETA release and currently supports following features: Clients, Client Projects, Project Invoices, Messages and File Attachments, Project Tasks which can be assigned to site users, Project Time Entries which can be assigned to site users
It is the original WP invoice and billing plugin which is now completely rewritten and re-released by its developers. Using this plugin you can create and send web-invoices and configure recurring billing for the clients. You may read its detailed summary of new features on its WordPress.Org Page. Following screenshot shows invoice status and progression. View more of its screenshots here.
It allows you to create and send web invoices, you can configure recurring billing for clients. It supports both single and multi WordPress installations. Following screenshot shows Invoice Overview, view more of its screenshots here.