Perhaps this uses DBpedia (<a href="http://wiki.dbpedia.org/About" rel="nofollow">http://wiki.dbpedia.org/About</a>)?<p>This is similar to the site Freebase (<a href="http://www.freebase.com/" rel="nofollow">http://www.freebase.com/</a>), which has a lot more data. Example node: India (<a href="http://www.freebase.com/m/03rk0" rel="nofollow">http://www.freebase.com/m/03rk0</a>).
This reminds me of "Nested" from Orteil, the creator of Cookie Clicker.<p><a href="http://orteil.dashnet.org/nested" rel="nofollow">http://orteil.dashnet.org/nested</a>
Could use another few iterations of the interface (I don't like the way the lists vanish right after they appear), but the concept and execution are first rate. I will be making regular use of this. Most semantic-web-like thing I've seen so far this year.
This site also summarizes what I hate in the current webdesign trends: broken back button and spurious event handlers attached to the not-quite-linky-links.
For almost all of my queries, this is just giving me the list of "categories" on the corresponding wikipedia page, leaving out the wiki-specific ones such as " Articles with Open Directory Project links", etc. Clicking the categories just opens the listings on the corresponding Wikipedia category page.
Quite possibly I don't understand what its doing or why, but I entered the word "stylus", meaning the needle on a turntable, and I got an opening suggestion of "writing implements", and the tree related only to that. So, unfortunately for me a bit of a fail. Like I say, perhaps I missed the point.
Really impressed with results for words like 'twirling', 'homoiconicity', 'ferromagnetic', 'mahler'.<p>Unimpressed by 'sandwiches', which surprised me.
Annoyingly, the contextual menu makes it impossible to open the wikipedia articles in new tabs. One solution would to have actual links (either text or icons) after each title.
Interesting visualization -- perhaps having a link to the wikipedia page for each item or using an iframe to display the wikipedia page would make it a bit more useful.