The category generator builds category specific archive pages for each category in your blog posts. The archive pages use the category layout (included with Octopress). In the _config.yml you may change the directory for the category archives if you like and the title for the category pages.

category_dir: blog/categories
category_title_prefix: "Category: "

If you visit a category archive for 'open source' the url would be /blog/categories/open-source/ and the title would be Category: Open Source.

This plugin was originally developed by Dave Perrett but it has been updated and improved for Octopress.