BonPatron is a website that serves as a French spelling and grammar checker. Although originally designed with a strong pedagogical focus for students learning French[1], it is now widely used by both Francophones and non-Francophones. The interface of the page is offered in both English and French (there's also a sister site for correcting texts in English: SpellCheckPlus.
French, from ExpressNews circa 2005] (Part of the University of Alberta)