Open Source Ruby Billing Software

OpenSourceBilling or OSB is a simple, open source web application for creating and sending invoices, receiving payments, managing clients, and tracking and reporting. There’s no need to pay for these services because OSB does it all for free and easily. OSB can produce reports of sales, payments and collected revenues, and simply makes billing and invoicing hassle-free. OSB comes with plenty of built-in features, such as recurring invoices, exporting to PDF, time tracking, receiving payments through Paypal and credit card, Freshbooks and Quickbooks data importing and more. It also supports several different languages as well as currencies.

This is a rental property management web app. At this point I'm writing it by myself for my mother, who is a rental property manager, but if it picks up steam great.