Process Monitor
Process Monitor is an advanced monitoring tool for Windows that shows real-time file system, Registry and process/thread activity.

Windows Performance Toolkit
The Windows Performance Toolkit (WPT, or xperf) is a free toolset from Microsoft that lets you see everything happening on your system in order to investigate otherwise invisible performance problems in your game. WPT can show Disk IO, registry access, GPU packets, page faults, context switches, kernel activity, and even has a sampling profiler, all integrated into one visualizer.

API Monitor
API Monitor is a free software that lets you monitor and control API calls made by applications and services. Its a powerful tool for seeing how applications and services work or for tracking down problems that you have in your own applications.

SpyStudio
SpyStudio shows and interprets calls, displaying the results in a structured way which is easy for any IT professional to understand. SpyStudio can show registry keys and files that an application uses, COM objects and Windows the application has created, and errors and exceptions