WordPress is a blog publishing system written in PHP and backed by a MySQL database. It is distributed under the GNU General Public License and is available free of charge. It has been downloaded hundreds of thousands of times to date.

WordPress.com is a WordPress powered weblog hosting provider. It runs WordPress MU, a less-customisable version of the software that allows people to create and manage their own weblogs without requiring the time, money and technical knowledge involved in setting up WordPress on an ordinary hosting account.

• Full standards compliance with the standards of the W3C
  
• No rebuilding  - changes  are reflected immediately on the site, with no need for regenerating static pages
• WordPress Pages  -  allow  managing non-blog content easily
• WordPress Links  - allows creating, maintaining, and updating of any number of blogrolls through the administration interface
  
• WordPress Themes -  makes designing everything from the simplest blog to the most complicated webzine a piece of cake
  
• Cross-blog communication tools -  fully supports both the Trackback and Pingback standards
• Comments  - visitors  can leave comments on individual entries, and through Trackback or Pingback can comment on their own site. Comments can be enabled or disabled on a per-post basis.
• Spam protection  -  an integrated blacklist and open proxy checker to manage and eliminate comment spam, and  a rich array of plugins that can take this functionality a step further.
• Full user registration
  
• Password Protected Posts
• Easy installation and upgrades
• Easy Importing
• XML-RPC interface
• Workflow --- one can have types of users that can only post drafts, not publish to the front page
• Typographical niceties --- WordPress uses the Texturize engine to intelligently convert plain ASCII into typographically correct XHTML entities. This includes quotes, apostrophes, ellipses, em and en dashes, multiplication symbols, and ampersands
• Intelligent text formatting
  
• Multiple authors  -  allows up to 10 levels of users, with different levels having different (and configurable) privileges with regard to publishing, editing, options, and other users.
• Cross-browser bookmarklets
• Ping away  - supports pinging Ping-O-Matic, which means maximum exposure of the  blog to search engines