Fluvial - a transit patronage visualiser
My local public transit authority, TransLink, releases origin-destination patronage data.
I found myself wanting to visualise patronage flows for specific routes, and so I built Fluvial.
The tool generates what I am going to call "rainbow diagrams" - we have a line with stops running from left (start of the route) to right (end of the route). Arcs representing patronage flows swoop overhead. With appropriate colouration, the effect resembles a rainbow:

Why "Fluvial"? Transit is like a river.