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.

Hunspell - Hunspell is the spell checker of LibreOffice, OpenOffice.

iThenticate - Prevent Plagiarism in Published Works

DSpellCheck - Yet Another Notepad++ Spell-checking Plug-In

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