Grammar Checkers

We all know about spell checkers, but fewer people know or use grammar checkers. There is one built into Microsoft Word. The only open source program I've found is Language Tool. I tried the practice window on their web site and the results, unfortunately, were quite poor, clearly worse than Microsoft Word's grammar checker.

The algorithms that go into these programs are by nature inexact, as it is very difficult for the computer to know the writer's intentions. Probably half of the suggestions are just plain wrong. However, the ones you can use may prove valuable, especially if English is not your first language.