Glassboard is an app for Android, Windows, and iOS phones that enables you to create and participate in private groups. Using the app you can create and participate in as many groups as you like. Kind of like when you use Google Plus, you specify which groups can see the content you share. You can share notes, links, pictures, and videos. The content you share and the content others share with you is displayed in a news feed on your mobile device.
Applications for Education
Glassboard, like Beluga that I reviewed last winter, could be a handy app to use when you take students on a field trip. By having everyone use the app you can quickly communicate important information like meeting times to everyone at once.