BillingFox

BillingFox is an all-in-one billing software made for hosting providers and domain registrars but not limited to other subscription based products, it have a list of features that include: automatic orders, help-desk, advanced management tools and more.
BillingFox can be 100% personalized and allows you to make your startup a successful one by reducing the costs and growing the customer experience rating.
As for developers, everyone can add new features to BillingFox by creating addons, themes & client area styles with an easy integration for every type of resource.