If you're looking for a writing tool that can catch grammar and spelling errors as you type, Grammarly is a great option. This AI-based tool offers personalized advice, context-specific suggestions and integration with many apps and websites. It also offers features like plagiarism detection, citation help and various pricing tiers for individuals, businesses and enterprises.
Another powerful option is LanguageTool, which supports more than 30 languages and language varieties. It offers detailed grammar checking, paraphrasing and tone suggestions. LanguageTool can be integrated with many writing tools and apps, so it's a good option for professional and academic writers who have to write in a formal style.