MovableType is a very popular, commercial WebLog system.

Until recently, it was free for most people, and for some classes of users it had been promised to always be. Then the licensing terms were changed and a lot of hoolabaloo ensued, because the promises were largely broken by the changes and a lot of casual users would have had to pay steep prices. The terms of license soon changed again according to feedback, so that few people who shouldn't be are affected anymore.

Nevertheless, it made many realize that non-Free software can be a trap, even if it's free and the SourceCode is available. (Just like RMS has been saying.)

Unfortunately, all GPLed replacements seem to be written in PHP. One of the better ones is WordPress.