Microsoft has rolled out a beta of their Live Writer application- and it is great! True WYSIWYG, including the themes, simple insertion of:
- bulleted lists
- numbered lists
- links (with several options)
Add offline caching and editing plus compatibility with Typepad, Blogger, Moveable Type, WordPress, LiveJournal and more- now you have a really good utility.
Not Open Source, but free (as in beer).