Reference: http://xkcd.com/149/

You can view this image and many other interesting photos at the Astronomy Picture of the Day website. http://antwrp.gsfc.nasa.gov/apod/ap090805.html

We never had childhood building toys when I was a kid. "You were lucky. We lived for three months in a paper bag in a septic tank. We used to have to get up at six in the morning, clean the paper bag, eat a crust of stale bread, go to work down t' mill, fourteen hours a day, week-in week-out, for sixpence a week, and when we got home our Dad would thrash us to sleep wi' his belt." You insensitive clod!

While this is not free as requested by the original askslashdot poster, I would also mention SnAppshot from Novell. It sounds like it will be exactly what he/she is looking for. I've used it in the past to snap an OS, install software or reconfigure something, and then snap again to list all of the registry and file changes. It worked really well and made it possible to script some automation into our task of configuring a large number of workstations.