USCIS now has a FREE app, “USCIS: Civics Test Study Tools" available or iPhone and Android.  The app helps you prepare for the civics test during the naturalization interview. It also has a game to challenge your civics knowledge, reminder notifications, and review of past tests. You can also switch between English and Spanish.
Be sure you get the official app! Follow the links above or search for “USCIS" or "USCIS civics.” Then, check that USCIS is the developer.