Liferay isn't just for intranets! Users and developers are building all kinds of different websites and systems based on Liferay.
An intranet is great for collaboration and information sharing within a company. An extranet extends this facility to suppliers and customers, who usually log in over the Internet.
In many ways, this is similar to an intranet—however, there are few technical differences. The main difference is that you create user accounts for people who are not part of your company.
Collaborative websites not only provide a secure and administrated framework, but they also empower users with collaborative tools such as blogs, instant e-mail, message boards, instant messaging, ...