NHunspell is a .NET version of the open office spell checker. Functions: spell checking, hyphenation, thesaurus with the open office dictionaries. It is free (GPL,LGPL, MPL) and can be used in closed source software. http://nhunspell.sourceforge.net

WarFoundry is an open-source, cross-platform, multi-system army creator for wargames of all types.

Written in C# (supported by both .Net and Mono), it currently supports both Windows and Linux with native UIs and is looking for developers, including those working on Mac OS X. The application will be extensible with plugins and support the loading of a variety of file formats....

Radegast is a light weight client for connecting to Second Life and Open Simulator virtual worlds.

DotGNU Portable.NET is a suite of free software tools to build and execute .NET applications, including a C# compiler, assembler, disassembler, and runtime engine. The system runs on a variety of platforms including GNU/Linux, Windows, Solaris, *BSD, etc....

Open Steamworks is an open implementation of the Valve's Steamworks API. In a sense it provides the same client only functionality you would receive if you or your company applied for Valve's Steamworks.

The Command Line Parser Library offers to CLR applications a clean and concise API for manipulating command line arguments and related tasks. It allows you to display an help screen with an high degree of customization and a simple way to report syntax errors to the user. Everything that is boring and repetitive to be programmed stands up on library shoulders, letting you concentrate yourself on core logic. The search for the command line parser for your application is over, with this library you got a solid parsing API constantly updated since 2005....

cript unit tests from the command line and from inside of Visual Studio. It also supports running in the TeamCity continuous integration server.

NoRM is a .net driver for communicating with MongoDB. NoRM is focused on "POCOs first", so things like String-typing and LINQ just work.

ImageListView is a .NET control for displaying a list of image files. It looks and operates similar to the standard ListView control. Image thumbnails are loaded asynchronously with a separate background thread.

ImageListView requires the .NET framework 2.0....

Gurtle is a TortoiseSVN issue tracker integration plug-in for projects hosted at Google Code.