The WP Social SEO Pro plugin comes in 2 Versions. There is a Lite (Free) Version which be downloaded here and there is the Pro Version which has a series of advanced features and capabilities which go beyond the Lite Version of the plugin. The WP Social SEO Pro plugin allows you to enhance and magnify the Social Media Signals and SEO transmitted from your Wordpress Blog to Social Networks like Facebook, Twitter, and Google Plus; along with easily configuring Google Authorship and Publisher status for you and other users of your Wordpress blog. It also enables the full use of Google Structured Data (Rich Snippets) on your blog, Image Optimization via the Kraken API, HTML5 Boilerplate Optimization of your .htaccess file, and more.
The SEO Booster Lite (Free) Version is limited to Posts on your Wordpress blog and does not have the advanced Google Plus and Advanced Twitter Card Optimizations as well as a host of smaller fine tuned optimizations not readily apparent from the outside looking in.
The power of the SEO Pro and SEO Pro Pro Plugins is the behind the scenes Meta Tagging, Rich Snippet, and Authorship/ Publisher attributes which allow Google, Bing, Facebook, Twitter, Google Plus, and other search engines and Social Networks identify and deliver content from your site in Search and through Social Sharing more effectively than you would be able to do otherwise.