Jeremy Miller asks an informal poll of people using Open Source Tools for .NET Development. The answer is a resounding yes, I/we do. Here are some of the tools I'm using or used in the past:

• NUnit
• CVS
• TotoiseCVS
• Subversion
• NAnt
• RhinoMocks
• The Castle Project (Windsor, in particular)
• NHibernate
• Log4Net
• WinMerge
• GVim
• CruiseControl.NET
• SharpDevelop
• Wix
• ... and more

Several of those I consider critical parts of my toolbox and wouldn't even dream of starting a project without them.

OSS, Tools