Serendipity

Serendipity is a weblog/CMS application allowing users an easy way to maintain an online diary, weblog or even a complete homepage. The application features a flexible framework allowing the user to work in HTML or WYSIWYG editing, multiple authors, multiple languages, spam blocking, one-click upgrade and the ability to embed in existing websites. Serendipity's plugin architecture makes it easy to modify blogs and their features. More than 120 plugins and 40 templates can be installed with just one click.

Homepage: http://www.s9y.org/