A very talented programmer called Tomas Pettersson spent 6 months creating an amazing Windows program which he called Sculptris. It is, effectively, a computer simulation of a ball of clay, which you can sculpt, prod, pull, poke, and generally manipulate with your mouse in order to create a sculpture.
The program then came to the attention of a company called Pixologic, and is due to be released as a commercial product at some point. Meanwhile, the version which Pettersson originally created is available as a download from Pixologic's web site and is completely free. It's officially a "prototype", so expect even more features when the full product launches.
The program is pretty tiny, and is just a 3 MB download. It runs on Windows XP and above, and you don't even need to install anything. Just download the zip file, extract it, then run the Sculptris file.
The link to the download is on the LAST LINE of the FIRST POST, on http://www.zbrushcentral.com/showthread.php?t=090617.
To see a better demo of what the program can do, rather than my best effort(!) as shown below, check out the Youtube video at http://www.youtube.com/watch?v=6DNRg6pdNeE.
Thanks to user Bosse Bergenholtz for finding this excellent download. Got any more Hot Finds? Tell me, at http://www.techsupportalert.com/content/submit-product-review.htm.