Many flight attendants don't have a regular schedule. Instead, they can browse upcoming flight itineraries and choose ones they are interested in. For example, a sample itinerary might be Chicago to Cleveland to Boston to New York to Chicago over a 2 day period.

All of these features are available in the internal applications provided by the airlines, but they're not always that easy to use or flexible. Obviously, as a flight attendant, being able to get notified of new itineraries, book quickly, and perform complex searches is a big advantage to getting better flights, so there is a small but very motivated market for custom apps like these.

Of course, these apps aren't supported by the airlines, so they operate in a grey area and use techniques like credential passing and screen scraping to get access to sensitive internal data.