I've seen various sites running on WordPress, whereby the visitor can set the skin by clicking on a link (typically in order to demo a theme).

For example, here is one I just came across. Notice how the "wptheme" parameter in the URL sets the theme to be displayed, and take note of the other themes available in the page's footer.

Is there a standard WordPress setup, plugin, or piece of software that will allow me to do the same for my site's visitors? Thanks!