Answer:
Grammarly
Step-by-step explanation:
You'll have to go directly to the website and type whatever it is your working on right there if you want to be able to have access to everything, because if you download it and use it on other things such as Google Docs the only thing it will do is add in punctuation where it is needed, and fix your spelling.
On the website though you have some more choices on how to change what your writing. Although I will be 100% up front with you, you don't have full access to all the features it has to offer unless you pay for a subscription.
I am a high school student, and I don't pay for it, so I don't have access to everything it has to offer, but the basic-free plan works well enough for me.
Hopefully I was helpful, if you need any other help feel free to let me know. Unless it's in math xD