I am the coordinator of a number of C# based open source projects on Bitbucket (as a replacement for CodePlex).
A quite popular tool to remove ghosted devices from the Windows Device Manager with a single click.
Like ghostbuster a quite popular tool to download whole (public) albums from Google Picasa without depending on a Picasa installations. Basically all you need to know is the picasa username.
A Forth Interpreter written in 100% C# (it's almost ANSI X3.215-1994 / ISO compliant). Due to the use of C# a number of low level features cannot be implemented (as it does not use the usual flat memory approach where forth can modify it does not implement features that modify programs and stacks in memory).
A tool to merge assemblies together or into an executable. I do not coordinate this project but maintain it (after a total rewrite of the existing basic code into C#).
The following C# projects are not publically available yet or anymore:
Latent Semantic Analysis
A port of my php_lsa php plugin project written Borland Delphi. The purpose of the library is to do LSA analysis on documents. It needs sparse matrix classes from Swiss Tools. Note: although running there are still some minor discrepancies between the Delphi and the C# version.
A library that enables a programmer to quickly generate a Wix Installer by running an application. Wix Builder can scan the target project for files (so can add new files automatically).
A collection of components I used in the other projects.
Electronic Workbook Editor
An editor to quickly generate course frameworks for both Blackboard and Moodle 1.9.x.