I just wanted to introduce my own project, Lucid Fried Eggs. It's not an outliner exactly, it's more of a non-hierarchical note-taking application. It's GPL and web-based, so it's free and works on any platform. It's written in PHP using MySQL.

Disadvantage: it's harder to see the big picture than with traditional outliners

Advantage: Any note can have multiple parents.

http://www.sourceforge.net/projects/lucid

http://www.memes.net

...Steve Danic
mailto:sdanic@memes.net