I remember posting about it here in the past, because I was so in love with the service that allowed me - a complete beginner - to get a case 3d-printed cheaply and easily.

The project itself is documented here:

https://steve.fi/Hardware/helsinki-tram-times/

It consists of an LCD-screen and an ESP8266 device. (Think "like an arduino, but with on-board wifi". Programmed in C++ it basically polls an online URL to decide what to display with a simple web interface you can point your browser at to change the timezone, the stop-id being monitored, etc.