At OpenTech a few weeks ago, Jeremy Ruston (creator of TiddlyWiki) demonstrated Project Cecily, a zoomable interface for TiddlyWiki. Now he's talked again at OSCON, and the demo is online for anyone to try out (requires Safari >= 3.1, as it uses some (so far) WebKit-specific features - note the video tag, for example).
Click to play (or download):
This is an exciting interface for presenting information, and may be a good interface for organising and creating/writing information as well. If you could draw edges or boundaries to group/connect items together, you might end up with a semantic mind map.
It would be good to be able to use web services to pull in information as well - that should be do-able with a TiddlyWiki plugin.