Automattic has launched "Jetpack," a new plugin which allows self-hosted WordPress users to enjoy several features previously available only to WordPress.com blogs. Jetpack also provides convenience features that don't use the cloud, but are now easier to install, or were unavailable as plugins before.
For launch the company has brought eight of the most-requested features into Jetpack as one easy bundle: Gravatar Hovercards, WordPress.com Stats, After the Deadline, Twitter widget, shortcodes, shortlinks, easy Facebook/Twitter/WordPress sharing buttons (Sharedaddy), and LaTeX markup.
The difference between the two WordPress.com & WordPress.org is:
On dot-com in just a few clicks you're set up on a web-scale centralized platform that constantly gets new upgrades and features. And you never have to worry about it because it's completely hassle-free and completely supported by our happiness team.
On dot-org you sign up and host your blog with a hosting company and you get complete control over every aspect of your plugins and code, but you also have the responsibility of maintaining it and adding anything new you want to try.
More Info and Download: Jetpack