Its offline, is extremely simple to organize your itinerary, comes with one-touch downloadable maps of the Underground, and even has an updatable calendar of events. BUY THIS APP! You will thank me! In fact, this whole companys series of city travel guides is extremely useful. I have the Paris, Rome, and Vienna ones as well. Again, its offline, so you need not worry about roaming/data charges. Cannot say enough good things about this app!
Julia Gulia79 about London Travel Guide Offline