SIW (System Information for Windows) is a free* software that shows a lot of information about your computer. Most of the data can be obtained by running different tools included in Windows, but this program displays everything in one place.
You'll get information about the operating system and the installed patches, the software licenses, drivers, Windows services, codecs, open files, saved passwords, hardware information (motherboard, CPU, memory, video card, ports) and some useful tools (like Eureka, that reveals passwords from some applications).
The software doesn't require setup, so you can copy it to your USB drive and use it when your uncle Dan says there's something wrong with his computer. You can export all the data in different formats and use the program from the command-line.
* The software is free (as in "free beer") for personal use.