http://en.wikipedia.org/wiki/Hunspell
- Despite its name, it is not for Hungarian alone anymore
- Open Source
- Run on Open Office
- Fairly well-known
- Probably less powerful than AfterTheDeadline/Polishmywriting.com
AfterTheDeadline
- Powerful, it can check style too
- Open Source
- Run on Open Office -(there is also a web-based version at Polishmywriting.com, but I could not achieve comparable results - browser-based versions exist too, making it legible for Google's OpenOffice, Google Drive)
- Well-known
- Still room to grow compared to some proprietary software (but here I am talking about spellchecker for French, not for English, so I can't compare)