I ran a home search startup in 2015 and I will always remember the moment my searching finally came up with the name "isochrone" and the explosion of research and data that came with that. Our home search went from "we'll send you an email when its done" to adding fake loading bars to make it seem like it was doing more.
I agree, Zillow has lackluster filtering. I’ve been working on something similar for people looking for remote work and aren’t particular about where they live. How did the project end up? What were the good parts and the bad parts?
GeoApify[0] is one of these commercial services using OpenStreetMap data. They have a no-friction isochrone "playground"[1] that's sufficient for casual exploration. You can switch the travel mode to "transit" to include train routes, but the maximum travel time for the demo is capped at one hour.
The results are very different, eg chronotrains-eu.vercel.app claims that Wittenberge is within an hour of Berlin Hauptbahnhof, but GeoApify won't take you further than Nauen. Possibly chronotrains-eu is showing a best-case travel time while GeoApify is attempting to calculate realtime travel using the current day's schedules?
I doubt the main OSM site would ever host an isochrone demo, as it's more of a reference implementation of very basic map and routing features that OSM data enables. Notably, the routing demos there do not (yet) include any kind of transit mode.
An isochrone map is one of the best tools for weekend get-aways, job hunting, and finding a home location.
OpenStreetMap[1]! Add it to your site, it will be great hit, in my opinion.
[0] https://en.wikipedia.org/wiki/Isochrone_map
[1] https://www.openstreetmap.org