Almost every traveller has used TripAdvisor to plan their trips - whether to choose a hotel, arrange an itinerary, or get more information on the destinations they're visiting. However, I found that many people aren't aware that TripAdvisor has an Offline City Guides app that can be used on your phone without any internet connection.
Think of this as a condensed version of TripAdvisor which you can download to your phone for the cities you're interested in. You have access to the hotels, attractions, restaurants, guides, reviews, and almost anything you need. The awesome part is the integration with GPS, which requires no data connection or SIM card. You can see your location on a map with the area around you, find nearby places and their reviews, and even use a 'point me there' feature to guide you to the place you select - like playing a video game, but in real life.
Download link: http://www.tripadvisor.com.sg/apps-icityguides