Wordpress is one of the most common CMS installations on the internet. Its famous 15-minute install is characteristic of its ease of use. But don't think its use is limited to blogging - it also has an extensive plugin selection making it an excellent choice for many different types of applications. For example, CSS Remix uses WordPress as an image gallery to showcase creatively designed websites across the internet.
Through its theming engine, WordPress can also be used as a social network (BuddyPress) and a twitter clone (Prologue), both which are open source. If you're looking to set up a simple site to keep in touch with friends and/or family, they're worth a serious look.
WordPress also scales well, and with a wordpress caching plugin like WP Super Cache, it can handle a high level of traffic. TechCrunch, a popular startup blog with nearly 1 million RSS subscribers employs WordPress.
WordPress's popularity is both positive and negative for webmasters. Its large and active community have created countless themes and plugins, through which one can highly customize a vanilla installation. However, its popularity has also made it the target of many attacks and exploits. If you choose to use WordPress be sure to keep up the installation up to date, although this is a good practice for any CMS. To make this painless, we recommend the WordPress Auto Update plugin. Its also important to look for updates to your plugins, which can contain security vulnerabilities as well.
One common problem that bloggers experience is comment and trackback spamming. As WordPress is so common, it has become a target for spammers. Fortunately, Automattic, the developer of WordPress, has created a solution in the form of a WordPress plugin called Akismet. The plugin transparently removes spam comments an trackback pings, which account for an alarming 88% of all comments on WP blogs (according to the Askimet website). Automattic does ask that commercial blogs earning at least $500/month purchase a commercial API key, starting from $5/mo.
Wordpress is written in PHP and licensed under the GNU General Public License, which allows for its use in most applications.
Homepage: http://wordpress.org
Download: http://wordpress.org/download/