Dawood Bin Abdullah Bin Saeed Al-Saqri writes English learning materials for learners at B1 to C2, many of them Arabic speakers. His Mastering English library covers vocabulary, synonyms and shades of meaning, grammar, writing and speaking, with clear explanations, real examples and practice you can check yourself. The books are on Amazon; this website is where you will find what Amazon does not have: Website Exclusive Editions, short focused PDFs on one skill each, and complete collections that put a whole series in one download at a lower price. Every title is built around the mistakes learners really make, levelled with the CEFR, written in British English with Arabic support where it helps, and comes with answer keys that explain why, not just what.