"By viewing the web through a tangle proxy, you can see the connections and associations left by those who surfed the web before you. By surfing the web using tangle, you also leave behind connections and associations for others who will surf in the future.
When you exit one page and enter another (by clicking a link or performing a search), a two-way link is created between the pages. As users surf through a particular page over time, tangle keeps track of popular ways to get to the page and popular places to go next. These entry and exit links are displayed at the top of each page, sorted by popularity.
Clicking on one of these entry/exit links tells tangle that you think the link is relevant and useful (like a vote for the link) and increases the link's popularity. In other words, if a user thinks of something relevant while reading a page and performs a search for it from that page, tangle gauges how others react to that association over time.
tangle is similar in some ways to the closed-loop hypertext system Everything2, though tangle works for the web at large.
We have several tangle proxies up and running. The tangle proxy software is also available for download.
A note for the paranoid:
Though tangle keeps track of web usage patterns, the focus is not on tracking the habits of individual users, but on tracking the trends of an entire community of users. tangle is GPL'd open source [source here], so you can see for yourself: clicking a link through a tangle proxy simply bumps up the links popularity---user IP addresses are completely ignored."