I hope nobody minds my saying here that I have posted a Release Candidate of Opal http://www.a-sharp.com/opal/ If you don't have a Macintosh, you can still look at the screen shots. (I'll add more if there's something you're curious about.)

Opal is a single-pane outliner, and currently has a single column, which can contain styled text with embedded graphics.

If you do have a Macintosh, you can try it free for 30 days.