Jetpack is an opensource WordPress plugin that adds many site management tools including visitor stats, security services, performance improvements, and syndication options. Jetpack functionality is pre-built into WordPress.com hosted websites.
The development version of the plugin can be found on Github.
POSSE using Jetpack Publicize
Jetpack includes a Publicize function which one can use to POSSE to a variety of silos (Facebook, Twitter, Google+, LinkedIn, Tumblr, and Path) with minimal configuration required. It also has excessive and clear documentation.
Its dashboard can be found at http://example.com/wp-admin/options-general.php?page=sharing by replacing example.com with your personal domain name.