<p>Is there any good bug tracker based on .NET which is free?</p>

Two bug trackers I know:
BugTracker.NET
BugTracker.NET is a free, open-source,
  web-based bug tracker or customer
  support issue tracker written using
  ASP.NET, C#, and Microsoft SQL Server
  (or its free cousin, SQL Server
  Express).
BugNET
BugNET is an issue tracking and
  project issue management solution
  built using the ASP.NET web
  application framework. Email
  notifications, reporting and per
  project configuration of fields and
  values allows efficient management of
  bugs, feature requests, and other
  issues for projects of any scale.