How it works
BTCPay Server is a self-hosted and automated invoicing system. When checking out, the customer is presented with an invoice. Each time, a different address is tied to a particular invoice, so there is no address re-use. BTCPay follows the status of the invoice through the blockchain and informs a merchant when he can fulfill the order safely.
BTCPay is a code, not a company. There is no third-party between a merchant and a customer. Merchant is always in full control of the funds. There are no processing or subscription fees. BTCPay Server is free to use and completely open-source, so developers or security auditors can always inspect the quality of the code.
Source code: https://github.com/btcpayserver/btcpayserver