Process Explorer, also known as procexp.exe, shows you information about which handles and DLLs processes have opened or loaded.

WinDirStat is a disk usage statistics viewer and cleanup tool for various versions of Microsoft Windows.

Shell Tools, a collection of free shell extensions and utilities like FontLoader, CopyURL, Filenote, Fresh Icons and others

"SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are placed on your devices. Treemap concept was invented by Prof. Ben Shneiderman, who kindly permitted the use of his concept into this tool."

"Tired of debugging your regular expressions ? Do you want to quickly build efficient regexps ? Visual REGEXP is for you ! This software will let you design your regexps by letting you type the expression and visualize its effect on a sample of your choice."

"Incredibly simple meters that live in the Windows 7, 8 and 10 task bar.Three applications are included: One that shows CPU utilization, another that shows memory and the third shows disk IO."

"andLinux is a complete Ubuntu Linux system running seamlessly in Windows 2000 based systems (2000, XP, 2003, Vista, 7; 32-bit versions only). This project was started for Dynamism for the GP2X community, but its userbase far exceeds its original design. andLinux is free and will remain so, but donations are greatly needed."