Another favorite tool of mine is Edmodo. Unfortunately the site is blocked for the district I work for but I have used the site for various graduate classes I have taken. It can be used for educating students or it is also great for professional development. Here is a quick video one how it works. Edmodo Tutorial
This video gives ways you can use Edmodo in a classroom.
This video gives a brief overview of how Edmodo can be used for professional development in a school district.