Grammarly is a browser plug in for the Chrome browser which provides spelling and grammar advice. A spell and grammar checker on steroids. On my main writing workstation, I have Grammarly loaded and running all the time. It almost feels like a part of the underlying browser, but with nice bells and whistles.
I am currently working on a book for Packt, and we have a sweet content development portal. We just go to the web site and use the text editing features to enter the text and graphics. We can then output to PDF - it works well. Inside this CDP, Grammarly is wonderful!
When I am entering content in the CDP, you can see Grammarly when it has something it's not happy with, like this:
In practice, I write and insert code/pics, then repeat and repeat. I touch type, but not with perfect accuracy. For me, at least, it's faster to leave a typo in the sentence and continue typing than to fix the error then carry on. I can then just use the mouse to fix the errors - and that works well for me!
The free version is excellent. But for a fee, there's a Professional version that adds a significant number of additional grammar checking rules, including passive voice as well as a plagiarism checker. The Pro version is billed either monthly ($US 37.95), quarterly ($US 24.98), and annually ($US 11.66). At the moment, there is a 20% reduction - but I do now know how long that will last - with the discounts the prices are $29.95, $19.98, and 11.66 per month).
On the downside, several of us have noticed that with Grammarly turned on, our content deployment system can crash. This is a pain, but regular saves, autosave turned on, and bit of experience - recovery is usually pretty easy. I can live with the occasional hang in exchange for such a great product.