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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
You can build this using Sabre and Amadeus APIs. There are other GDSes, but those are the two largest. It won't be a cheap app to build, and you have to pay for access and use of the APIs, and to get access you may need to become a licensed travel agent, etc... but it's doable. Alternatively you may be able to build on top of an existing OTA like Expedia using their APIs. There's probably not a lot of margin though.
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