MiniBill is a great Open Source program for a small-medium business. It uses Authorize.net for recurring billing, and has great reporting capabilities and is easy to program and make custom addons and plugins. We're striving to keep the core of MiniBill as basic as possible, so you can download plugins as you need instead of having a boatload of featuers you DON'T need. Visit our site, see the demo, download MiniBill!