If Facebook and Blackboard had a baby- it would be edmodo
Edmodo is a great tool to use in the classroom. It is easy to use, quick to get started, and students really like it. You can also set up small groups so students can collaborate on class projects online. It is available on all platforms and their new snapshot tool is AWESOME - you can create assessments aligned to common core standards and see a dashboard to analyze how your students are doing. Oh...and it's FREE!
How I Use It
I have used edmodo as a supplement to a face-to-face class, and to facilitate a completely online course. I have also used edmodo to facilitate a department PLC and to facilitate professional development sessions/trainings.