Duffel is interesting, I wonder what they use on their back end. I've written airline booking API when I was at an OTA (now sadly gone like so many) on top of o

Duffel is interesting, I wonder what they use on their back end. I've written airline booking API when I was at an OTA (now sadly gone like so many) on top of our parent company's res system. It can be complex, made more in my case so by the pathetic res system itself and its limitations. In fact at the time we had no way to do test bookings without real money (and mostly un-refundable except for a single route).