This site may not be flashy, but it is useful! An extensive collection of interactive quizzes in areas of frequent grammatical confusion awaits. This is a compilation of the work of several highly respected educational institutions and publications.
This site is a great resource for review of the six writing traits. It includes explanations, rubrics for scoring, and examples for each trait. While the site includes the option to create an account for an interactive experience, this is not necessary to use the basic resource (and I will not be creating a classroom account).