Windows experts named Mark Russinovich and Bryce Cogswell have started writing simple but useful tools in 1996. They are provided these tool in those books related with Windows system internals. These tools became popular and released by them.
They can be downloaded from a lot of alternative locations but their official repository is
Sysinternals suit provides tools in the following categories.
- File and Disk
- System Information
Tutorials about following tools can be found in this site.