Grammarly works on google docs, that's what I'm always using. I also use inLinks for on-page SEO with entities/topical relevancy.
Still considering using surfer SEO, but at the moment it's just on my wishlist.
Doing tests with NLP, but don't have much traffic going in to actually have conclusive results.
I've been using NLP in real life though for 4 years now. It does produce magic in a lot of circumstances. People are easy to manipulate. Trying to do it for articles too.