Grammarly is an AI-powered writing assistant that offers personalized advice, context-specific suggestions and integration with many apps. It also has a plagiarism detector and citation tool. Grammarly's pricing options range from free to premium, so you can find something that works for you.
Another powerful tool is ProWritingAid, which has a lot of AI-powered features, including style advice, real-time checks and readability analysis. It can be integrated with Microsoft Word, Google Docs and Scrivener, so you can use it in whatever writing environment you prefer.
If you need to write in multiple languages, LanguageTool is a good option. It checks grammar and offers paraphrasing in more than 30 languages and dialects. It also offers plugins for various writing tools and standalone apps for Windows, macOS, Linux, Chrome OS and Android.