CK12 is a great platform that allows you to access tons of digital resources and share them with your students. Here is a screenshot that shows you the variety of resources you can find:
As you can see, you have text resources, videos, activities, assessment and more. To learn all about it, visit their tutorial center for short instructional videos and how-to's. CK12 is also fully integrated into Edmodo, so you can utilize this for assigning (workflow). Yay!!