Soundgrammar.com is a free online resource for students that focuses on teaching how grammar is used. Each of the thirty lessons contains a short conversation that highlights how grammar expresses various meanings, an audio transcript (which you can hide), some grammar notes and a quiz.
I've no idea who is behind Soundgrammar.com as there's no FAQ or 'About'. The website design is pretty basic and I could find no trace of the 'Mobile Content' or 'Printable Lessons' which are mentioned. However, the lessons themselves are actually quite good. The dialogues are well recorded, and the grammatical explanations are easy to follow. Add in the quiz, and you've got a nice resource for lower level learners of English who need some basic grammar revision.