The classic transport and logistics mogul OpenTTD has a lot to offer if you love trains, boats, airports, highways and other examples of extensive infrastructure. Free and open source, OpenTTD has an extensive registry of maps, modifications, graphics packages and more to use. The recent release of the game on Steam is making some people get to know or learn its wonders for the first time.
Me? I'm very interested in this giant map of Europe. It is 8192×8192. This is 8192 ^ 2. This is … this is very large. It's all over Europe with a bit of North Africa, most of Turkey and a lot of Russia. It was made by Korean OpenTTD player tiram2sue and friends and I love it. It's so big you can't see everything in a screenshot with a maximum zoom. The map is optimized to work with JGRPP, an OpenTTD version. You can find it via tt-forums.net.
Anyway, I'm going to create an OpenTTD multiplayer server. He will rule. It should only take a few thousand hours to fill this beast with a map. That is, of course, after spending ten hours deciding on train sets and graphic packages. You can find OpenTTD through your dedicated official website i and Steam.