Update October 2014: Unfortunately Glassboard has shut down.
Glassboard is a private social network. In Glassboard, you create ‘boards’ which are groups of people around a common interest, and you can share messages, comments, photos, videos, files and even your location (when appropriate). It has apps for iOS, Android devices, and the Web. Glassboard describes their difference to Facebook Groups this way:
The focus of Glassboard is to give you privacy. In the app there is no element of discovery, unlike in Facebook where you can search for anyone and subsequently add them to a group. Facebook Groups are easy to get people on board since so many people you know are already on it, whereas Glassboard is a much smaller social network and you’ll likely have to invite people as new users. There is a minimal amount of information about you gathered in Glassboard (we just need your email address and what you’d like to be called) whereas Facebook not only gathers the information you’ve provided for targeted advertising, but also your behavioral patterns. Also, with Glassboard all of your data is encrypted on the back-end. Glassboard has a different business model to Google+ and Twitter. It is funded by paid subscriptions, rather than acquiring revenue by mining your data to sell advertising. Glassboard currently has about 200,000 users. A free account allows you to create up to three “boards” with 100MB of storage per board. The cost of a premium account is $24.99. With this account you can create unlimited boards, and you get 1GB of storage per board. Link: Glassboard