Chyrp is a blogging engine designed to be very lightweight while retaining functionality. It is powered by PHP and has very powerful theme and extension engines, so you can personalize it however you want. The code is well-documented, and it has a very strong structure that's loosely based on the MVC design pattern.
Customize look of URLs, or use the recommended Clean URLs
Easily add and edit pages
Save posts as drafts for later editing and publishing
Easy HTML blog posting
Tons of modules to add functionality to your blog
Clean interface with AJAX
Add comment feather to add a comment system to blog