Paul in 3rd Interaction pointed me at this nice topic map editor. I would say its pretty much the best one I've seen so far. First think its not written in Java, which doesnt bother me that much but does sometime have a effect when you have a large and complex diagram. It saves as SVG natively and imports/exports to XTM and a range of image formats. Its just a shame it doesnt import or export RDF but we all already know the massive aurguements happening in the semantic web community about RDF and XTM. So until that day I'm forced to transfrom between them and lose certain meaning and use other editors for RDF such as this one I found a while ago. The other one worth a mention which I use to use is, freemind which promises to have topic map and svg abilities soon.
Oh by the way I also saw this on plasticbag a moment ago, which is kind of related. It links to this pdf which shows Tom Smiths thought about social software.
