Can I create a Drupal site, where a user, let's call her Jane, can create an account and publish some content, like a few articles. Then create accounts for her friends who can login and view all the nodes she has created, and which they create. At the same time, Paul creates an account, creates some nodes, and invites his friends etc. However, Paul and his friends cannot see Jane's nodes or users - and vice versa. It feels to Jane and Paul that they have there own separate website.
What are the key Drupal concepts or methods for creating a site like this? Thanks.