Samuel Mello

This plugin was designed to create virtual micro-sites that employ different themes while using the same content from one source. It uses WordPress’s rewrite rules to decide which theme to display to the end user based off of the url they visit. This will allow you to access the same website in a virtual sub-directory with a completely different theme displayed.
REQUIRES PRETTY LINKS TO BE TURNED ON

Cameleon

Virtual Microsite Creator & Multi-Theme Enabler for WordPress

John P. Bloch

Create child themes from any non-child theme with the click of a button.
This plugin is multisite compatible; if used on a multisite network, controls for creating child themes will be in the network admin instead of the regular site admin. Pick the parent theme from the dropdown and name name your new child theme. You can also change the author name and select files you want to copy from the parent to the new theme.
Click the button and you’re all set!

Child Themify

Create child themes with the click of a button.

Cameleon vs Child Themify