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.

Aby Rafa

Show meta description in your homepage, single post and page. This plugin helps you to attract visitors and boost traffic. Just plug and play. (WordPress Simple SEO – Meta Description).
If you want to know how this plugin works, right click on your page and then select view page source. You will see your meta description between the header tag.
<ul>
<li><a href="http://wp.labnul.com/plugin/one-meta-description/" rel="nofollow ugc">Plugin Homepage</a></li>
</ul>

One Meta Description

Show meta description in your homepage single post and page. (Wordpress Simple SEO - Meta Description).

TagMeta vs One Meta Description