Estive recentemente em Paris e estas apps deram muito jeito:
https://play.google.com/store/apps/details?id=net.ixxi.ratp.tourisme&hl=pt-PT
https://play.google.com/store/apps/details?id=com.fabernovel.ratp
https://play.google.com/store/apps/details?id=net.ixxi.ratp.tourisme&hl=pt-PT
https://play.google.com/store/apps/details?id=com.fabernovel.ratp