LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
iThenticate - Prevent Plagiarism in Published Works
Gramlee.com - Online grammar check, proofreading and copy editing services.
Plagramme - Our plagiarism checker recognizes paraphrased plagiarism, checks your paper against more that 14 trillion documents and lets you to edit your paper online.
Grammarian PRO3 - Grammarian PRO3 is a feature-rich grammar checker that enables you to write better content without taking assistance from the English teacher.
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.