As wikipedia defines it - “A web content management (WCM) system is a CMS designed to simplify the publication of web content to web sites and mobile devices, in particular, allowing content creators to submit content without requiring technical knowledge of HTML or the uploading of files”
Here are some good Open Source ASP.NET Web CMS that are popular in the community.
Update: Kentico has a free ASP.NET Web CMS too and can be downloaded over here
N2 CMS - N2 is a lightweight CMS framework to help you build great web sites that anyone can update. Using it's interface is intuitive and empowering. It is based on an object model with separation between view templates, content model and database and integrates well with the ASP.NET and ASP.NET MVC 2 paradigm.
DotNetNuke Community Edition - DotNetNuke, also known as DNN, is the ideal platform for building professional websites with dynamic content and interactive features. It is the most widely adopted Web Content Management Platform for building web sites and web applications on Microsoft .NET.
mojoPortal - mojoPortal is an extensible cross platform, cross database, content management system (CMS) and web application framework
Umbraco CMS - Umbraco is an open source Web CMS for .NET. Its flexible content model with full .NET integration, full control over markup and stellar user interface makes both editors, designers and developers smile.
TheBeerHouse CMS - TheBeerHouse is a website developed with Microsoft's MVC Framework which includes a number of features and modules that you expect from a typical CMS / e-commerce website, such as Membership, CMS, Opinion Polls, Mailing List, Forums and much more.
Kooboo CMS - Kooboo is a web CMS built based on ASP.NET MVC framework. It is designed for those organizations or people who need enterprise level content management and fast web development
My Web Pages Starter Kit - The My Web Pages Starter Kit is a dynamic content management system (CMS). It is designed to meet the needs of computer enthusiasts who want to deploy and maintain their own website – and it is also easy to modify the look and feel or even change/extend the feature set
Cuyahoga - Cuyahoga is a flexible CMS / Portal solution written in C#. It runs on both Microsoft .NET and Mono and uses NHibernate for persistence Multiple databases are supported
So the next time you want to create a CMS without paying a dime, you would now know which ones to try out! You can Bookmark this link for future use.