From the front page:
pMachine is online publishing's most flexible and creative software. With pMachine, you can publish virtually any kind of web content - from a basic weblog, to an advanced interactive magazine. pMachine gives you complete control over the presentation and the interactivity of your site.
pMachine was my first blog. I was running phpwebsite as my "main" website, but found myself posting to pMachine all the time. It's very flexible, meaning that the code is all worked down into function calls, making it easy to design your HTML page and then add in a few PHP tags here and there to display the blog/category/etc. content.
It's downsides are that it's not free. Non-commercial users can use the "Free" version, but must pay for the Pro version (which includes forums). Commercial users must always pay. Also, not being open source, it doesn't seem to develop as quickly, nor does it sprout a lot of add-ons and plug-ins.
Fine if all you want to run is a basic blog.