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Grammarly - Clear, effective, mistake-free writing everywhere you type.
Plagramme - Our plagiarism checker recognizes paraphrased plagiarism, checks your paper against more that 14 trillion documents and lets you to edit your paper online.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
SCRiBBR Plagiarism Check - This plagiarism check uses the best of both worlds.
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.