If you are familiar with SOS.dll, the managed-debugging extension that ships with the .NET Framework, Psscor2.dll provides a superset of that functionality. Most of the added functionality helps you identify issues in ASP.NET.
For example, Psscor2 provides the ability to view:
* managed call stacks (with source mappings)
* managed exception information
* what types are in the managed heap and their reference chain
* which ASP.NET pages are running on which thread
* the contents of the ASP.NET cache
* and much more.
Read more: Jin's WebLog original, translated
Download: MS Download