London's Oyster card is one of the oldest single-card payment systems for metros in the world, and the venerable card is working to stay ahead of the curve with the new TfL Oyster app. The app allows users to conduct much of their account chores on their mobile devices rather than at the payment terminals in the station, saving time and reducing lines.
Through the TfL Oyster app, users can top up their cards anywhere, as long as they have an internet connection. The app also provides a host of features that would surely be convenient to most regular London Underground riders, including the ability to check one's trips over the last eight weeks (and thus track spending) and notifications for when one's account is getting low.
The TfL Oyster App Makes It Easier for Tube Users to Stay Topped Up
References: itunes.apple & engadget