gaxx

Automatically adds keywords and description meta tag on every page based on title, tags, categories, etc.
It works on the basis of defining some simple, tag-based rules for different page types (home, category, post etc).
Built on the foundations of the excellent Automated Keywords Generator by Julian Widya Perdana (http://mr.hokya.com/automated-keywords-generator)

Gaxx Keywords

Automatically adds keywords and description meta tag on every page based on rules that draw information from title, tags, categories etc

xenice

Xenice SEO is a simple, fast, and lightweight SEO plugin designed to give you precise control over meta descriptions and keywords for every post, page, and taxonomy.
Unlike heavy SEO frameworks, Xenice SEO focuses on the essentials — helping search engines better understand your content without slowing down your website.

Xenice SEO

A lightweight SEO plugin that allows you to add meta description and keywords fields for posts, pages, categories, and custom post types.

Gaxx Keywords vs Xenice SEO