Writing is difficult enough before the editing process, and often your mind corrects errors that you've made because it knows what you intended to say. It's useful to have a set of fresh eyes to look over and proofread a document so that you can find hidden errors, and Grammarly provides a set of 'eyes' to help with that. It's an add-in assistant which helps you correct errors in spelling and grammar on the fly, with helpful suggestions for which alternatives to use. There is a paid version that allows you to edit on a more precise level, but the free version is fairly robust and effective. It can also tell you why your original text is incorrect, so it really has a number of in-class uses for a history student or educator.
For instance, history classes generally require several papers a term. We often ask for properly edited papers with excellent spelling and grammar, but we don't always provide ideas for tools which can help a student excel in those areas. Grammarly is one tool that I can use as an aid for students in choosing proper writing and editing. I can also use it to show my students why one writing choice might be preferable to another. In both cases, I'm going to be receiving papers that are written and edited well, which is giving my students a better chance for success in class. It's an add-on for most internet browsers, can be installed to the desktop, several writing apps and integrated into Microsoft Office.
Watch this short tutorial for basic instruction in using Grammarly, and see how you might make use of it.