jBilling is a web-based enterprise billing system.
jBilling is a web-based enterprise billing and rating system. It manages your subscribers with automatic invoicing (email and PDF) and payment processing (credit cards, checks, direct deposit). Robust, well documented and easy to use!
Znode E-commerce Integrator is a C# Library for Payment Processing, Shipping & Accounting Integration. Currently supports Authorize.net, Paymentech Orbital and Paypal payment gateways. You can also retrieve shipping rates directly from UPS.