Make your writing (almost) perfect with editor
As a writer and an editor, I have a love-hate relationship with Serenity Software's Editor (various pricing; ten-day free trial). This copyediting and proofreading application not only identifies common grammatical errors, but also thoroughly analyzes your writing for other weaknesses. I love that it focuses on good, solid writing. I just hate the fact that so many folks–myself included–actually need it.