Timo Schlueter

TagMeta generates meta keywords using your most used tags. 
It automatically gets the 10 most used tags out of your 
blog posts and pages and puts them into a valid meta- 
keyword string. This string then appears in the header of 
the home page of your theme. If you want to add tags per 
post, i suggest youre going to use the Headspace plugin.

TagMeta

TagMeta generates meta keywords using your most used tags.

Dejan Batanjac

Creates meta description write panel for posts pages and custom post types. 
Meta description write panels are not present in the default WordPress installation.
Meta description were traditionally important for website SEO. Today, with the improvement of the software that reads and summarizes the textual documents, they are loosing the importance.
Still you can find them useful on pages with low or even no text.

SEO Meta Description

Creates meta description write panel for posts, pages and custom post types.

TagMeta vs SEO Meta Description