Luke Rumley

This plugin allows you to assign a theme to a specific category. It is actually @MikeLopez’s code, I just tweaked it to work on WordPress 3+.
This version adds child theme capability, and the ability to assign a theme to a new category as it is created. It also ignores pages and the home page, so the current theme is applied there.

GYS Themed Categories

This plugin allows you to assign a theme to a specific category.

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.

GYS Themed Categories vs Child Themify