Edmodo

Edmodo allows the discussion to continue even after that school bell rings. Teachers and students can share content and use the app as a conduit for new information or notifications, submitting assignments and receiving grades in the process. The ability for teachers to post assignments, messages, polls and quizzes, while providing access to relevant resources and calendars, is simply invaluable.

https://www.edmodo.com/

Edmodo is a tool that I actually learned about in Library school, my classmates and I used it for class projects and to share things while actually sitting in class. This was outside of the instructor, but it is designed to be structured and managed BY an instructor and can be incredibly beneficial if you use it in a structured, class specific way. Fantastic tool with tons of functionality.