The Writing Assistant Grammarly
Its simplest features, such as grammar and spell check, are free for all whereas the more advanced assistance comes with a monthly fee. You can use Grammarly for instance as a browser plug-in, web based editor or a Microsoft Office add-in. The tool learns to give more accurate response through AI and deep learning along with its users information about what kind of text they're writing and which audience it's aimed towards. Errors, possible problems and suggestions are highlighted in colour in order for the user to spot and understand the mistakes more easily.
Read more about how Grammarly works or try it out in their editor.
How Grammarly works:
Try the web based editor: