See: Matka.fi API
Helsinki Region Transport HSL
HSL is transport authority in Helsinki region. Area includes 7 muncipalities: Helsinki, Espoo, Kauniainen, Kerava, Kirkkonummi, Sipoo, Vantaa.
Available data sources
Journey Planner HTTP Get interface. The API server has the most recent timetable data provided by HSL.
Kalkati.net, XML database dump. The dump file represents the line, route, and timetable data of the HSL timetable database exported into a single file.
My Departures HTTP Get interface. Stop timetables.
Disruption Info HTTP Get interface. Disruption info bulletins.
HSL Live HTTP request and push interfaces. Real time location of vehicles. At this point system includes all trams and some other lines.
Helsinki region open data catalogue. https://hri.fi/fi/
City of Tampere open data
City of Tampere upkeeps catalog of open data sources: http://data.tampere.fi/