Grammarly is a free software to help students check their usage of grammar [and plagiarism; I believe with the upgrade which costs money]. Teachers can use Grammarly for their own work, and to have students pre-check their own work, which saves teachers countless hours of time providing feedback to students about their grammar. This shifts the given feedback towards the content of the writing instead.
To improve your grammar, try the following games:
Disclaimer: this is only for use with the English language.