Cluster – Private Spaces For You and Your Friends
https://cluster.co/

Create a group space, add the people you care about, and watch those people join and contribute. Features include: a) Private & Secure – Only invited members of the space can see what you post; b) An App for Everyone – Award-winning apps for iPhone, iPad, Android, and Web; and c) Relevant Notifications – Know when people you invited post new things to the space. This will be added to Privacy Resources Subject Tracer™ Information Blog.