I have been addicted to this game ever since I downloaded it on Sunday!!!
Its called Open TTD (Transport Tycoon Deluxe)
The aim of the game is to build a transport network for a whole heap of isolated town and mini cities on this big map.
The game starts off in 1950, and then the years go by and with those years new types of vehicles become available, and towns are becoming bigger, the game ends at 2050. Like in real life.
You can build, bus networks, train networks, ship and plane.
Here are some shots/photos
(ps. the shots on here look worse than the actual game, because I had to make them smaller to fit on this page)
The map starts like this in 1950:
And hopefully ends up like this in 2050
I'm currently up to 1970 with bus networks in all towns and starting building on a train line covering the whole map

Thanks,
PLI