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.
Grammarly - Clear, effective, mistake-free writing everywhere you type.
iThenticate - Prevent Plagiarism in Published Works
WhiteSmoke - WhiteSmoke software products for writing and language. WhiteSmoke is a grammar checker, spell checker, style checker and more - in a single package. Also featuring translation software and English video courses.
Urkund - Detect and check for plagiarism with URKUND