LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
iThenticate - Prevent Plagiarism in Published Works
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.
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.
PlagScan - The Internet makes plagiarism a bigger problem than ever.