Edmodo about a year ago through a workshop I attended. It has been a fantastic addition to my Professional Learning Network (PLN) and a great source for ideas and solutions. According to Edmodo, they "provide teachers and students a secure place to connect and collaborate," reaching over 7 million educators and students globally. But it is just so much more.
I have used it to connect with communities I am interested in as well as join groups that are formed for more fine-tuned specialties. You can create groups (public or private) and share resources via a library, create polls, quizzes, assignments, notes, alerts, and more.
It is a great way to teach with Social Media for your students: facilitating discussions, feedback through polls, or using assignments and grading on the go. Edmodo is web based and offers mobile apps so everyone can access the site. A plus for students! My colleagues test drove it in our middle school classes this year and the response was positive--and the kids loved it!
Following that success, we decided to change our school PLN to the site to facilitate more sharing among our teachers. We used the last part of our faculty meeting to get everyone into the computer lab to sign up and into our Group. So far it has been a place where idea and resource sharing is building!