https://www.whmcs.com/

Web Hosting Automation Made Easy. All the tools you need to start a web hosting business today. Save Time: WHMCS takes care of automating things so you don't have to, saving you valuable time and money. | Automate Billing: Sending invoices, collecting payments, taxes, reminders and more are all a thing of the past with WHMCS. | Web & Domains: Integrated with all the leading web hosting control panels and domain registrars for automatic provisioning and management. | Support Tools: Integrated support tools give you a client portal complete with ticketing, knowledgebase, downloads and more. | Developer Friendly: Modular, extensible, well documented API's and ORM all make developing with and customising WHMCS easy. | Secure & Scalable: WHMCS is a secure, dependable and scalable solution designed for businesses of all sizes and backed by an awesome support team.