I'm searching for a tool that would make real-time suggestions based on "real world" text. The only corpus-based tool I know of is Writefull - does anybody know of any others?
There is Grammarly. It is an app which can be used to check spelling and grammar typed into a browser; whether it is for webmail, website contact form or blogging site. It can check your grammar when typing a question or answer here.
There is also a Grammarly plugin for use with Microsoft Office.
Grammarly is a great tool for grammar problems (hence the name) and thus works across the board for many types of writing. If are doing any fiction writing, check out AutoCrit. You pay a monthly cost to use it and enter your story directly into the web browser and it brings up problems in your writing like using too many adverbs, lack of sentence length variation, etc.