What is a Content Management System (CMS)?
A content management system is software that keeps track of every piece of content on your Web site, much like your local public library keeps track of books and stores them. Content can be simple text, photos, music, video, documents, or just about anything you can think of. A major advantage of using a CMS is that it requires almost no technical skill or knowledge to manage. Since the CMS manages all your content, you don't have to. Easy Web Content can provide economic CMS solutions to you quickly.
DotNetNuke
DotNetNuke is an open-source 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 200,000 users, and a dedicated base of programming professionals, support for DotNetNuke is always close at hand.
Joomla!
For those of you who prefer a non-windows alternative, the top PHP/MySQL CMS is Joomla!
It's an award-winning content management system ,
which enables you to build Web sites and powerful online applications. 
Many aspects, including its ease-of-use and extensibility, have made Joomla the most popular
Web site software available. The Joomla! community of programmers have created 'bolt-on' extensions to handle anything
from event management to video short competitions.