Sorry folks, know this post is way-late, unfortunately I've only stumbled upon the discovery not too long ago. Anyway, Returnil is a sandbox application. It creates a sandbox around your system. When this sandbox is enabled any changes made to the system are made within the sandbox. These changes have no effect on the underlying operating system and are not apparent when the sandbox is disabled. Returnil also creates a persistent virtual drive to store files while the sandbox is active.
Returnil is not for everyone as it requires a bit of tech savvy and many may not have a need for it. It however is very good for the developer and tester as it isolates possibly harmful effects and protects your system from damage as a result of something gone horribly wrong. It also very good for those like myself that evaluate lots of software with no intention of keeping it all : )
__________
The free license is available via a GHacks promotion, i.e. their GHack's Christmas Giveaway. Like the Avanquest Advent Calendar, free software licenses will be given away everyday up till Christmas. Unfotunately, most giveaways have been a first come first serve kind of deal and are therefore no long valid. The Returnil offer is available for everyone and expires beyond the Christmas day deadline, January 2, 2009 (HST/GMT-10/Hawaiian Standard Time) to be exact. Well if you are into this kind of thing be sure to get a license.
Yesterday's offer was Fast Picture Viewer. Which seems to be a very useful piece of software for those in need of a fast image viewer with features no professional photographer can do without. This too is a giveaway for everyone but time is of the essence. The offer expires on Monday at 10:00 UTC. The serial key provided will not register after that time.