In addition to knowing which payment system, I'd love to know if Uber actually redid the work of credit card transactions from relative scratch, or if they just used something like Stripe or Braintree.
I'm relaly impressed with the diversity of their offering as well:
https://www.adyen.com/pricing/full-list
I'm currently in Japan and it's actually relatively common to pay for things at the convenience store here, I'm amazed they support it.