[Symbiote]

The London version is now an app. I think it used to be available as some kind of map.

http://www.tubeexits.co.uk/

[genmon]

It's also a feature in Citymapper. Only front/middle/back but the integration means I use the information more often

https://citymapper.com/news/726/where-to-get-on-the-train