I got an invite a few days ago to a new social networking site which you can create for your organization. When first logging it, you may think you are actually using Facebook since the site is very similar. It has many of the same social features but also seems to combine aspects of other social networks such as Google+, Linkedin and Twitter.
If you have always wanted to use a Facebook like site for your school or class but can't due to it being banned, Yammer may be a great alternative. It encourages collaboration among all members of the school community, in a way which is private and secure. The site also has mobile apps which help you to stay connected on the go.