Movable Type, a great blogging platform similar to WordPress.org, has just released an open source version.
Although Movable Type is similar to WordPress.org (it's non hosted, meaning you need to install it on your own Web host, and the features are quite similar), it's suffered from complex and expensive licensing, whereas WordPress.org has always been free.
Reportedly the open source version is not quite ready for prime time yet, and paid versions continue to exist.
Why would you pay for something you can have for free? Many reasons, but the biggest is usually support. Free software doesn't come with a support contract or guarantee.
This is big news for Movable Type AND users of WordPress.org -- the competition can only make WordPress better, and Movable Type will get a lot larger user community as well.
Movable Type is owned by Six Apart, who also owns TypePad (which this blog uses). Movable Type and TypePad are similar, but not identical. One massive difference is that TypePad is hosted, meaning that there is no Web host to configure or software to install -- it runs on their servers.