"is an Apache mod_perl handler that uses XSLT to transform XML Bookmarks Exchange Language (XBEL) files into exciting and foofy dynamic HTML documents. Documents are rendered as collapsible outlines and individual nodes may be viewed and bookmarked as unique pages, so you don't have to click through a gazillion nested leaves to find what you're looking for." I made this! You can play with a live demo, that uses XBEL as a sorta/kinda aggregator for RSS feeds, over here, but there isn't much point unless you've got a 5.0+ browser.