I’m pleased to see Belgian grammarian Monsieur Grevisse well-represented on Archive.org, with several works available for borrowing, including but not limited to Le français correct, Le bon usage, Quelle préposition, and Savoir accorder le participe passé. There is even what appears to be a downloadable recent edition of the venerable Le bon usage, though it is certainly still in copyright so there’s no telling when it will be removed.
French Study Blog 