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

Wordpress is an open-source project, which means there are hundreds of people all over the world working on it. (more than most commerical platforms).  It also means you are free to use it from anything to your cats home page to a Fortune 5 Web site without paying anyone a licence fee.