Stripe, Square, PayPal, Bill.com and Melio are not the same kind of product. Invoicing is a record you can own. Card acceptance is a network membership. ERPNext, GPL-3.0, can raise the invoice, track it, and sit next to a processor. It cannot become the processor.
Why is Invoice Ninja not on this page?
Invoice Ninja publishes source under the Elastic License, which is not an open-source licence. We do not hand a client that tree and call it ownership. The invoice belongs in a system whose licence lets them keep running it, which is why the default is ERPNext.
What do you still pay a processor for?
Card acquiring, disputes, and payout to a bank. Those fees do not go away because the invoice is self-hosted. Anyone who sells open source as a way to stop paying card fees is selling a fiction.
When is the whole stack rented on purpose?
When invoicing volume is low and the processor's hosted invoices are good enough. Own the invoice when it has to match inventory, tax, and the customer record you already hold.
What do we hand over?
We select the system, deploy it on infrastructure you control, connect it to the tools you keep, and write the runbook so your own team can operate it. Support after handover is optional. The rest of the map is in software you can stop renting; the engagement behind it is open-source business systems.
Name one process that still needs a person. We will tell you what a one-time build takes.
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