Open Source .NET CMS

List is pretty big but here are a few.

 

Orchard 

Umbraco CMS

N2 CMS

Graffiti CMS

Composite C1 CMS

TheBeerHouse: CMS & E-commerce StarterKit

DotNetAge -a lightweight Mvc jQuery CMS

Koobo0 CMS

ASP.NET MVC CMS ( Using CommonLibrary.NET )

DotNetNuke® Community Edition

ASP .NET MVC CMS (Content Management System)

EPS content management (cms)

Boogaloo - A site creation framework & CMS

http://hydrogencms.codeplex.com/