Grammarly - Clear, effective, mistake-free writing everywhere you type.

iThenticate - Prevent Plagiarism in Published Works

LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.

Turnitin - Turnitin is preferred by educational institutions around the world for preventing plagiarism. Instructors at all levels of education can request that students use the service to submit papers, and Turnitin checks those papers for plagiarism.

Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.

PlagScan - The Internet makes plagiarism a bigger problem than ever.