I just pushed cl-creditcard to my github account. CL-Creditcard( and sub-library cl-authorize-net) is a library that we use to process payments with Authorize.Net. We have a large internal application that tracks and manages all our business and customer logic including billing and invoicing. (Invoices are generated using cl-typesetting). This application charges credit card payments through this cl-authorize-net.
It has been stable and charging cards for years and I just got around to releasing it. Soon it will also support ACH (echeck) transactions and we will be moving to lisp-unit from lift.
As with all payment processing, test very well before putting into production :)