WordPress

WordPress is a state-of-the-art semantic personal publishing platform with a focus on aesthetics, web standards, and usability. What a mouthful. WordPress is both free and priceless at the same time.

WordPress started in 2003 with a single bit of code to enhance the typography of everyday writing and with fewer users than you can count on your fingers and toes. Since then it has grown to be the largest self-hosted blogging tool in the world, used on hundreds of thousands of sites and seen by tens of millions of people every day.

WordPress homepage: http://wordpress.org/
The latest stable release of WordPress : http://wordpress.org/download/
Getting Started with WordPress: http://codex.wordpress.org/Main_Page
WordPress web hosting: http://wordpress.org/hosting/

WordPress Plugins Directory: http://wordpress.org/extend/plugins/
WordPress Themes Directory: http://themes.wordpress.net/