Yapta

If a user likes a given flight, Yapta will track that flight and notifies them if the price of the flight drops below the user's designated desired price. If the user purchases the ticket, Yapta will continue to track the price of the ticket.If the price drops, Yapta can alert the user to the possible availability of a credit or voucher for the airline, based on the difference.
Yapta offers indirect purchase of airline tickets through the airline websites. This enables users to purchase their tickets without incurring additional travel-agency fees.It is not at ticketing agency that offers direct purchases, such as Orbitz or Travelocity.
Yapta also offers a small application called the "Yapta Tagger". The Tagger works within the internet browser and when it recognizes an airfare displayed on an airline's website, it displays a "Tag It With Yapta" icon next to the price.Pressing this icon enables Yapta to track the flight as if you had searched for it on the Yapta website.
Yapta is an acronym for "Your Amazing Personal Travel Assistant."
Currently, Yapta supports price tracking for, at least, the following airlines:
United Airlines
American Airlines
Delta Air Lines
JetBlue Airways
US Airways / America West Airlines
Continental Airlines
Frontier Airlines
Alaska Airlines
AirTran Airways
Midwest Airlines

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