The self-study German grammar workbook: rule on the left page, exercises on the right.
About this tool →Details
Cornelsen's series covers A1–B1 in one volume and B2–C1 in another, with 85 short chapters, visual explanations, level-appropriate vocabulary and audio/video accessible free via the PagePlayer app. The layout is built for working alone, and answer keys are included. Written in German throughout, so absolute beginners will want an English-language grammar alongside the first chapters.