Grammarly

Grammarly is a writing assistant that checks spelling, grammar, punctuation, and clarity in real time across nearly any app where you type, including Gmail, Google Docs, Slack, LinkedIn, and Microsoft Word. It runs as a browser extension, desktop app, mobile keyboard, and web editor, underlining issues as you write and suggesting fixes you can accept with a click. Beyond basic proofreading it flags tone, wordiness, and readability, and can rewrite sentences to sound more formal, friendly, or concise depending on the audience.

It's used by students, professionals, and anyone who writes a lot of email or documents and wants fewer embarrassing typos without hiring an editor. The free tier covers core grammar and spelling checks, while paid plans (Premium, Business, and an Enterprise tier) add full-sentence rewrites, plagiarism detection, brand tone controls for teams, and deeper style guidance. Grammarly has also folded in generative AI features for drafting and rewriting text on demand, moving it from a pure proofreading tool toward a broader writing companion.

What sets it apart is sheer ubiquity and integration depth: it works inline across the browser and desktop rather than requiring you to paste text into a separate tool, and it's been around long enough (since 2009) to have become the default spell-check many people expect on any device they use.