A free app for Android, by Magoosh.

If you want to master the English language, this app can help you. The concept is simple: memorize commonly used grammar patterns. You will be able to improve your writing and speaking skills.

The app is based on a spaced repetition system, which is a well-accepted method for learning new information. The idea is to review the information more frequently, if you remember it well. This will allow you to master English grammar quickly and effectively. 

If you’re not sure how to memorize a pattern, just review it once. If you still don’t remember it, review it a second time, and a third time. Afterward, you will be able to recall it with ease. The app will help you learn English grammar.