Motorcycle Theory Test Lite is a great reference app. It was designed for motorcycle drivers who need to take the theory test to get their driver's license. The app includes a very thorough Highway Code, which is a guide of safe practices and security tips for drivers of all vehicles. It deals mostly with what to do in case of accidents, steps to take, etc. The two main modes are Practice and Mock Test. In Practice mode, you can select one of four available topics and have the application ask you questions about that topic. You are asked 20 questions per time. And after you are done answering them, the app will tell you how many you got right and wrong. You can even see the correct answers for each question. The Mock Test mode prepares a test that is very similar to the one you will have to take. It has 20 questions as well and you have one hour to complete it which is plenty of time.
Motorcycle Theory Test Lite has lots of information, but it is a free version of a more complete app: Motorcycle Theory Test, which contains 14 topics. The lite version has only 4. Other than the number of topics included, the two versions are identical.