ASP.NET Open Source Projects

Blogs

• dasBlog
• BlogEngine.NET
• SubText - A blogging engine in ASP.NET
• Owlpal - Web Content System

Content Management Systems

• DotNetNuke
• N2CMS
• Umbraco
• sharpcms

Controls/Toolkits/Frameworks 

• AJAX Control Toolkit - A control library for ASP.NET built over the MS AJAX Extensions for ASP.NET
• ASP.NET 3.5 MVC
• Gaia Ajax - an Ajax Framework for ASP.NET. Write C# or VB.NET; no JavaScript skills necessary
• CSS Friendly Control Adapters
• RIAnimation - jQuery Animation library in ASP.NET
• Enterprise Library - application blocks from the patterns and practices team
• Rich Text Editor
• CSLA.net - Rocky Lhotka on CSLA.NET and ASP.NET

• Castle Project

Forums

• YetAnotherForum
• PunBB.NET

Starter Kits

• TheBeerHouse: CMS and E-commerce Starter Kit
• Paypal eCommerce Starter Kit
• Small Business Starter Kit
• Personal Site Starter Kit
• Club Site Starter Kit
• Codeplex Club Site Starter Kit
• Extended Club Site Starter Kit
• My Web Pages Starter Kit
• Time Tracker Starter Kit

Wikis 

• FlexWiki
• ScrewTurn Wiki 

Miscellaneous

• ASP.NET 3.5 GeoTwitter Alpha Released
• BugTracker.NET - An ASP.NET based bug tracking application
• BugNET - Another ASP.NET based bug tracking application
• Digg like site Kigg using MVC
• DinnerNow
• DropThings
• Live Chat Support Open Source
• SplendidCRM - Full-featured CRM written in C#

 Additional Projects

• http://asp.net/community/projects/