Unfortunately AFAIK there are no open source projects that major credit card vendors and banks are willing to work with. That's the fault of the banks and cc vendors, not the vendor you are shopping at of course.

You might be interested in strike. It's not open-source but it's built on open-source protocols:

• Send and receive USD and BTC to more than 60 different countries, seamlessly convert between the two. Low or no fees depending on what you're sending/receiving and where. Vastly cheaper than western union and other remittance services.
• Transactions settle in seconds thanks to lightning network (there's your open-source protocol)
• Ability to scan QR codes to make or receive payments, or create QR codes to request them. Basically works as a point-of-sale.
• You can top-up or drain your account much like venmo (link to debit card or bank account) and you get your own unique username which you can change whenever you want.