Grammarly.com is a free/subscription web-based application that is described as "an online service that quickly and easily makes your writing better and makes you sound like a pro, or at least helps you avoid looking like a fool.” See Grammarly.com quote from Forbes. I signed up for the free version some time ago and it has been running on my Chrome browser for some time now. I guess since I write so much, that this app is now pretty much related to my genealogical efforts. I have had a long standing rule not to do "reviews" of programs but after considerable thought and lot of frustration, I decided to make an exception for Grammarly.com. So, this post could be construed as a product review.
For me, the most obvious effect of having the program on my browser is that it automatically flags misspelled words and "incorrect" comma placement. It also occasionally finds "wrong" word usage. The program works in the background so once it is added as a browser app, you do not have to turn the program on or off. It does have some limits and will not work with text documents outside of typing in online programs. At this level, it is helpful in the sense that my wife does not make as many corrections to my posts as she did in the past. Some of the frustration also begins at this level, since I do make a lot of typos and comma mistakes and it is always coming up with interruptions to my train of thought. I have several times thought about dumping the program, but I realize its utility and keep it functioning.
Now, to the heart of the issue: the program does not recognize a large percentage of my perfectly good sentence constructions. In short, its level of English grammar is very limited. I would guess that I ignore almost as many suggested "corrections" as I use. This most likely comes from my expansive definition as to what is and what is not grammatical in the English language. More simply put, my narrative style is not considered grammatically acceptable by the program. It is impossible for me to give an example because I do not think the same way the program is designed to correct. The program seems to have a very limited corpus of English usage. If you used every suggested correction, you would sound like you were writing a Freshman English paper.
Considering what I see online, I would suggest that many online contributors need the program. On the other hand, I would strongly suggest that using any "grammar" type program will inevitably end up being frustrating if you have been writing for some time. By the way, the program could probably use a shot from corpus.byu.edu.