Extranet

An extranet is a private network that uses Internet technology and the public telecommunication system to securely share part of a business's information or operations with suppliers, vendors, partners, customers, or other businesses. An extranet can be viewed as part of a company's intranet that is extended to users outside the company. It has also been described as a "state of mind" in which the Internet is perceived as a way to do business with other companies as well as to sell products to customers.
An extranet requires security and privacy. These can include firewalls server management, the issuance and use of digital certificates or similar means of user authentication, encryption of messages, and the use of virtual private networks (VPNs) that tunnel through the public network.
An extranet could be described as two or more intranets with network connectivity. Generally, and as with intranets, an extranet will be based on Internet Protocols. The underlying network technology does not really matter, for instance it may be that organizations use the Internet for carrying data but restrict access to resources from the general public via firewalls. A virtual private network could be set up over the Internet to achieve the same result.
An argument could be made that "Extranet" is just a buzzword for describing what institutions have been doing for decades, that is, interconnecting to each other to create private networks for sharing information.
During the late 1990s and early 2000s, several industries started to use the term "extranet" to describe central repositories of shared data made accessible via the web only to authorised members of particular work groups. For example, in the construction industry, project teams could login to and access a 'project extranet' to share drawings and documents, make comments, issue requests for information, etc. Specially secured extranets are used to provide virtual Data room services to companies in a number of sectors.
There are a variety of commercial Extranet applications. Some of which are for pure file management, others include broader collaboration tools and project management tools.
Some Extranet Product examples are:
Ace Project, Hot Project, Creative Manager.