GnuCash is personal and small-business financial-accounting software, freely licensed under the GNU GPL and available for GNU/Linux, BSD, Solaris, Mac OS X and Microsoft Windows.
Invoice Ninja is a free, open-source solution for invoicing and billing customers. With Invoice Ninja, you can easily build and send beautiful invoices from any device that has access to the web.
InvoicePlane is a self-hosted open source application for managing your quotes, invoices, clients and payments. The application comes with various options, templates and settings to customize your invoicing experience.
Send, track and collect payments quickly. Great for teams, freelancers and service providers. FreshBooks is an easy cloud accounting app for small businesses and freelancers, specifically designed to save you time billing clients.
Elorus is the time-tracking, invoicing & project management solution for professionals & agencies. Focus on innovation & reap the fruit of your labor.
Invoicera is an online billing software which is specifically designed keeping simplicity and online invoicing convenience in mind, while at the same time offering the best of the breed invoicing features.This app doesn't have any features at the moment.