isochrone.ch is an interactive web app illustrating public transport accessibility in Switzerland. Pick any starting point and it shows you where you can go within a given amount of time. This is quite useful in a country with such an amazing public transport network where most people don't own a car (people can typically use it to find new hiking or skiing destinations, when searching for a new flat, etc.).

The innovation here is that the transit routing logic runs on the client; I wrote a little open source library (minotor.dev) implementing the RAPTOR algorithm in TypeScript and optimizing timetable data (GTFS from https://opentransportdata.swiss) to be shipped to the browser. This enables super responsive visualizations as no round trips to the server are needed.

I built it on my free time and published the first version early 2025 but kept improving it since then (range query support, altitude filters, memory optimizations, etc.).