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

techphernalia

This plugin helps your SEO by adding meta keywords tag to each page, post, archive (category, tag, date, day and year). 
Now it also allows you to specify common keywords to be included on every web page. Plugin from one of the best coder <a href="https://www.techphernalia.com/" rel="nofollow ugc">Durgesh Chaudhary</a>. 
For any support just leave your question at our <a href="https://www.techphernalia.com/meta-keywords-generator/" rel="nofollow ugc">Meta Keywords Generator</a> page.
Uses Title, Description, Categories, tags, Compulsary keywords (provided by you in setting) for keywords generation. Uses content after striping short codes and short tags for generation of description.
Reduces manual work of adding them manually.
Now more efficient by allowing you to add one time master keyword list.
A big Thanks to Omer Barlas for suggesting to change text box to textarea for better readability.

Meta Keywords Generator

Adds Meta keywords and Description to each and every page, post, archive.

Gaxx Keywords vs Meta Keywords Generator