Grammarly - Clear, effective, mistake-free writing everywhere you type.
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.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
iThenticate - Prevent Plagiarism in Published Works
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
Urkund - Detect and check for plagiarism with URKUND