[tarstarr]

(I work on Stripe Billing.) Broadly we think most people should buy rather than build here, because billing is infrastructure and doesn't create the unique value in your product that makes more customers willing to pay. Why is there relatively little OSS for it? Probably because it's difficult to do right, a bit crufty, and tough to motivate a volunteer workforce to wake up in the morning and crank through some tickets about German invoice formatting.

Here's the evolution that we see at a lot of companies as they grow: the table stakes version of billing ("just get something that lets us charge for our MVP!") is an N week project. Everyone gets it wrong, but right enough to not kill the business. Then it worms the way into the rest of their systems, because of a lack of clear design boundaries or a documented internal API to answer questions like "Should account X have access to feature Y?", and it becomes an ongoing maintenance task both for the billing system and all the code which touches it, which is everything.

Once your business gets big, billing isn't just annoying and taxing on your productivity: you have to start telling the business "No, you can't do that, because the billing system won't support it and we can't fix that in less than 6 months." There are products which are not available in Japan because billing systems hardcode currency formats. There are marketplaces that can't tolerate cross-border commerce because they can't accept a pay-in and pay-out with different currencies, as a purely technical limitation.

These are not good problems to have. We think startups should just adopt a billing system which was written by a team of people who breathe billing issues. We feel so strongly about this that we subsidize startups use of our billing product down to free, for their first million dollars in sales.

There, of course, exist other options. As someone who works on this every day: please adopt one of them. You will save yourself a lot of toilsome work which largely doesn't advance your business goals.