One of the many uses of WooCommerce is to create a membership site. Using a few extra plugins, you can create premium content that's only available to users who have purchased the correct products from your site. The nice thing about this setup is that, if you want your membership site to sell any products, it's really easy to add that functionality, whereas a typical membership plugin will only allow memberships.
You must have WooCommerce Subscriptions, Groups (free-of-charge on WordPress.org), and Groups for WooCommerce (premium, available at WooThemes.com) installed and activated on your site. You should also have a Simple subscription product already created.