Blurb from the web page:

The Smallweb Subway is an experimental project that seeks to connect communities online using webrings.

[...]

The subway system theme is my attempt at making the internet feel more like a place where you can have neighbors. If a webring looks like a subway line, then it's easier to imagine a friend only a few stops away!

I really like this visual, and being able to see different topics on their own "lines." This feels like such an intuitive design, I hope it gets copied or riffed on elsewhere.