A free, web-based word processor, spreadsheet and presentation tool that allows you to create and edit documents from anywhere and collaborate with multiple people at the same time.
When collaborating with students, it's always best for the teacher to create the doc, then share it with students. This will avoid any issues in which the doc is erased from the student's account, the collaboration settings are changed, or other avoidable problems having to do with ownership rights.
Although documents can be shared with up to 200 people, documents may be edited/reviewed by up to 10 people at one time.
Spreadsheets may be edited/reviewed by up to 50 people at one time.