BitDisk 7 is a popular application for keeping your computer in the perfect state.
After BitDisk7 is installed on your computer, all and any changes that take place thereafter are not registered; instead, they are stored in a special container on the hard drive and are removed after reboot, bringing the computer back to its original "perfect" state, including all the installed programs, stored files, personal settings, and even position of the shortcuts on the Desktop!
Now you can do whatever you want: Infect the computer with viruses, erase the system files, remove programs - everything will get back once the computer is rebooted.