Aggie
Aggie is a news aggregator: it is a desktop application that downloads the latest news and displays it in a webpage.

Atom.NET
Atom is a new syndication format (similar to RSS in functionality) but aimed to simplify the task with a simple and clear specification. Atom.NET is an open source library entirely developed in C# aimed to handle Atom feeds in an handy way. It provides an object model to write and parse Atom feeds. It's compatible only with the 0.3 Atom draft specification. It works under MS .NET 1.x and Mono 0.29 and later.

FeedExpress
FeedExpress is a freeware and OpenSource (LGPL license) RSS feed reader. FeedExpress basically lets you subscribe to several RSS/RDF sources, known as Subscriptions in FeedExpress, in the same way that Outlook Express lets you subscribe to several news groups. FeedExpress caches and indexes all the feeds for each RSS subscription, making it easy to overview all your feeds.

GtkSharpRSS
A RSS and RDF client written in C# using Mono, Gtk#, and RSS.NET. It also has the ability to display content with an embedded Mozilla window.

mail2rss
mail2rss is a .NET web service that checks your mailbox on demand and returns an RSS feed containing the unread messages in it. The service is written in C# and uses .NET framework.

Nolior EZNews
Nolior EZNews is a tool for presenting news, announcements, information and more on a web site. Features are: XML storage, Control panel, User registration, Two user levels, Date ranges, RSS syndication, e-mail and more. Written in ASP.Net.

NRss
NRss is an open source Microsoft .NET Framework / Mono class library for reading a RSS feed into a tree of objects mapped to elements in the RSS feed. For example, there's a Rss class encapsulating the feed, a RssChannel class encapsulating the <channel> element, a RssChannelItemCollection class containing the items in the channel and so on.

RSS Bandit
RSS Bandit: an RSS/Atom aggregator for your desktop written with the .NET Framework.

RSS.NET
RSS.NET is an open-source .NET class library for RSS feeds. It provides a reusable object model for parsing and writing RSS feeds. It is fully compatible with RSS versions 0.90, 0.91, 0.92, and 2.0.1, implementing all constructs.