The _only_ grammar checker that I ever found tolerable was Grammatik IV (DOS) back in the 90s. At the time XyWrite was the wordprocessor of choice in my law firm. Even then, I usually ignored it. Over the years, one of the first things I do with a newly installed copy of Microsoft Word is disable both grammar and spell-checking, finding both annoyances and unhelpful. Instead, I rely on hard copies of Strunk & White's _The Elements of Style and Webster's _New World Dictionary_ that are always within easy each. Microsoft flagging two spaces after a punctuation mark? Barbaric.