I'm looking for an Online Billing Solution along with a Customer Portal in open source space so that I can customize it the way as required in future. My requires are: Flat & Subscription(Periodical) based Billing (orders/invoices) Able to set products/services, its prices add customers or customers can register themselves from client end (a web page) and mange their profile themselves from customer portal, pay online, order products, check invoices, cancel order / subscription, etc. An interface (web service or API) that would provide a mechanism to check when customer recieves service, his current status and then allow them access to the services (similar to subscription membership website ) Please provide me with the options I should consider.