Train Lord (TrainLord.com) is a live massively multiplayer game (MMOG) using real world data and maps. The goal is simple: become the richest lord in the world by buying rails, stations, trains, creating rail sets and dispatching trains.
Train Lord is playable at TrainLord.com. You can log in using Facebook, Google, or Twitter. It seems to be safe to use Twitter without it posting stuff.
Gameplay / manual screencast video with captions is available on Youtube. The video shows the main objectives you must accomplish in order to rule the game.
Train Lord gameboard is a world map. By default it uses MapQuest open tiles (OpenStreetMap), and offers alternative basemaps from various providers including several other OSM options. The railway data - rails and stations that you can buy in the game are from OpenStreetMap.
The OpenStreetMap data used in Train Lord is from October 2012.
'Introducing Train Lord' blog post gives more technical details