Give access to your content only to those who are willing to support you by sharing it with their friends
Imagine you have a newsletter and you want to share an ebook with your readers. To gain access you ask them in return to share the link with a couple of friends. It doesn't cost them anything, you get a lot more exposure to people who are probably interested in your content. Virale allows you to create these links easily and for free.
Only you, and no one else. Without any limitations you will be able to view and download the email list of users who have used one of your links.