Grammarly

The OG AI writing assistant, now with a full generative AI layer. Grammarly checks grammar, tone, clarity, and now generates entire paragraphs, rewrites passages, and adjusts formality level. Over 30 million daily active users across 500,000+ teams. The browser extension works everywhere — Gmail, Slack, Google Docs, LinkedIn, Twitter — making it the most ubiquitous AI tool by integration points. The free tier catches 90% of errors; Premium ($12/month) adds tone detection, full-sentence rewrites, and plagiarism checking. Grammarly processes 50 billion suggestions per year. For non-native English speakers, it's transformative.