Learn English Grammar is a free app for all levels, from beginner to advanced. It has a great interface that's very easy to use, with hundreds of lessons to help you improve your grammar and boost your vocabulary.

There are different kinds of lessons, like the ones that teach you the basics of English grammar, such as the structure of the sentences, or how to use the correct tense. There are also more advanced lessons that teach you how to use complex sentences and phrases, how to use the different types of English grammar, and how to express your thoughts and feelings in English.

Each lesson is short and easy to understand, and it has a great layout that will help you memorize the lessons better. You can use the app as often as you like, to keep improving your grammar and vocabulary.