Doctopus is a way to do this via Google Docs. It's a script where you can send out a template document (it can even be a blank document if that's where you want your students to start). The beauty of this is that you are the owner of the document and therefor students can't easily share their work with other students because they don't have that permission. Other things I like about it is that you can easily send students an e-mail once you have graded their assignment.
Before you start you'll need a spreadsheet with each student's name and e-mail address. This will later be where you can add additional comments and grades to be sent to the students.
This video below should help you understand this more, but if you have any questions please let me know and I will do my best to clarify.
