Site states - GroupTweet enables 2 to 100,000+ contributors to tweet from the same account. No longer is the burden of content creation on one person's shoulders. Contributors' names can be hidden or displayed at the beginning or end of each Tweet. Whether you have a small group powering a company account or thousands of people powering a group account, you can leverage the power of the crowd with GroupTweet!
Site states - Yammer is a simple, scalable solution that lets employees share and connect with coworkers in a private, secure enterprise social network. Collaborate in teams, see what your colleagues are working on, share ideas and get feedback, create and edit content, and receive updates from other enterprise applications - all in one place. - Good for educational setting as well.