WordPress (or rather b2 Cafelog) started out as a web blog tool in 2001. 14 years later WordPress now powers over 20% of the Internet, including websites like BBC America, Xerox, Best Buy and the Dallas Mavericks.
WordPress was able to make this transformation because their framework is extremely scalable. You can create a simple blog with WordPress, or it can become a huge e-commerce-driven website with the additions of plugins, themes and a great development environment.
WordPress is now the most used content management systems and powers the websites you visit every day.