Steam now offer early access to Tracks - The Train Set Game, a railroad construction game for Windows. Rather than simulate the real trains, or the elaborate electric physical train set hobby, this takes a further step, and nostalgically recreates children's wooden push trains. Here's a video showing this in action, and here's more on gameplay:

Track Building
Build the train sets of your childhood dreams with an easy-to-use editor. Just indicate where you want to build and Tracks does all the hard work for you, effortlessly mapping out turns, junctions and crossings under your command.

• Add houses and trees to create your own little villages
• Place unique track shapes and configurations beyond what you would normally find in a physical train sets
• Physics objects to play with
• Play in free-mode to build at your leisure without any set objectives

Ride the rails
Once you’ve created your rail network, you can ride along from inside your train, in first person. You’ll have full control of your vehicle in this view and will be able to adjust the train’s speed and direction. Your train’s weight and momentum are simulated, challenging you to maintain a steady but efficient speed while transporting passengers.