The AppVerifier focuses on two specific categories of tests: tests 
difficult to perform due to vendor system limitations and subtle 
problems difficult to diagnose on Windows XP Professional. Its purpose 
is to help vendors write stable applications on Windows XP Professional 
and future versions of the Windows operating system.  The latest version 
of the AppVerifier is included in the Application Compatibility Toolkit.

The Application Compatibility Toolkit for Windows XP contains documents 
and tools to help Windows customers diagnose and resolve application 
compatibility issues.  For the most recent release of the toolkit, 
see http://msdn.microsoft.com/compatibility.