An intranet is a private computer network that uses Internet protocols, network connectivity to securely share part of an organization's information or operations with its employees. Sometimes the term refers only to the most visible service, the internal website. The same concepts and technologies of the Internet such as clients and servers running on the Internet protocol suite are used to build an intranet. HTTP and other Internet protocols are commonly used as well, such as FTP. There is often an attempt to use Internet technologies to provide new interfaces with corporate "legacy" data and information systems.

Briefly, an intranet can be understood as "a private version of the Internet," or as a version of the Internet confined to an organization. (From Wiki)

In 1999 I was hired by Web Tone Technologies in Atlanta to build a corporate intranet.  I was the lead on a team of three and we built a system from scratch (far less functionality) what DNN has provided us. The DotNetNuke content management system features a user security and role based platform with a MS SQL server technology for small to large installations.

I can build in workflow management and publisher rights.  I can have the system operate as a company intranet, extranet and the company website all from the same installation.

DotNetNuke is an open-source Web Application Framework ideal for creating and deploying projects such as commercial websites, corporate intranets and extranets, online publishing portals, and custom vertical applications. 

DotNetNuke is provided as open-source software, licensed under a BSD agreement.  In general, this license grants the general public permission to obtain the software free-of-charge.  It also allows individuals to do whatever they wish with the application framework, both commercially and non-commercially, with the simple requirement of giving credit back to the DotNetNuke project community.

DotNetNuke is built on a Microsoft ASP.NET (VB.NET) platform, and is easily installed and hosted.  With a growing community of over 440,000 users, and a dedicated base of programming professionals, support for DotNetNuke is always close at hand.