Chargify is a recurring billing system designed for Web 2.0 and SaaS companies. Chargify allows you to concentrate on building innovative web applications and not worry about how to bill your customers.

Chargify does things like this for your business:

• Support for trial periods.
• Automatic proration if your customers upgrade/downgrade during a billing cycle.
• Reaching out to your customers to resolve problems if their credit card payments fail.
• Hosted pages for your customers to sign up and later to update credit card info.
• Coupon codes so your customers can get a discount when they sign up.
• Track units consumed by your customers and then bill them accordingly (think of text messages sent or sales leads purchased).
• Track "seats" used by customers over long periods of time, such as billing your customer based on the number of software licenses ("seats") they have or the number of hotel rooms they manage with your system, for instance.