Theme Tuner is a plugin for WordPress that allows you to edit in real-time the look-and-feel of your site, you can change a color, change a font, etc.
The authors, ChoppedCode have added 3 new extensions and 1 new widget in the current version. New extensions are being added, which are short codes you can place on your pages to for example add a widget area, as well as new widgets.
Plugin homepage: www.choppedcode.com
Download: http://wordpress.org/extend/plugins/theme-tuner/