While Visa and MasterCard are household names in the western world, there's a similar oligopoly (and similar history) in airline bookings system, which is largely unknown to people outside the domain.

Majority of worldwide airline bookings go through Amadeus/Sabre/Travelport, who similarly get a cut on each transaction. (The GDS industry has long been thought to decline _just in a few years_ but for now it still stays rather strong - although big airlines are actively trying to get more independent). The net incomes are about order of magnitude lower than credit card industry, but that's still hundreds of millions per year.