Act as a polyglot language instructor with 10+ years of experience teaching Russian. Recommend the top [NUMBER] apps for mastering Russian grammar, focusing on [BEGINNER/INTERMEDIATE/ADVANCED] learners. Highlight key features like [GRAMMAR DRILLS/INTERACTIVE EXERCISES/REAL-LIFE EXAMPLES] and explain how each app addresses common challenges like [CASE SYSTEM/VERB ASPECTS/GENDER AGREEMENT]. Provide a brief comparison of pricing models [FREE/SUBSCRIPTION/ONE-TIME PURCHASE] and platform availability [IOS/ANDROID/WEB]. Include tips on how to integrate these apps into a daily study routine for maximum efficiency.