I’m currently Working on a new feature packed WordPress theme framework and one of it’s features is the ability to select a custom theme template for a specific category,tag or custom taxonomy term, and a few weeks ago i saw a this question so i cooked up a little plugin from that class to do exactly that and published it as Custom Category Template plugin.
  

Screenshots:

What does it do?

This Plugin allows you to select specific page template per category just like with pages from within the admin panel.

How does it work?

When editing a category you will have a new field (just like in the above screen shoot) which enables you to select which page template you want to use for that category.
  

Main Features:

• Simple and lightweight.
• Easiest solution for category template ever.

Download:

Download the latest Version from WordPress.org

Simple Installation steps:

1. Extract the zip file and just drop the contents in the wp-content/plugins/ directory of your WordPress installation.
2. Then activate the Plugin from Plugins page.
3. Done!

this is it for now, enjoy and any feedback is welcome, also make sure to submit bug if you find any.
  

Change Log:

• 0.2
  • Quick bug fix
• 0.1
  • Initial release

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