In the good old days I used to play quite a bit of Transport Tycoon, an all time classic. It's a highly addictive game where you arrange the transportation in a small virtual world. You can use busses, trams, trains, boats, airplanes or helicopters to get the passengers and goods transported around between the cities. Its fun already to play alone since while playing it, it always gives you renewed thoughts on how to make your transportation network even more efficient. You can also compete against others online or play in coop style.
I have my own open Transport Tycoon server running on the internet for whoever feels like playing a round. If you want to use it, download Open Transport Tycoon for free, install it and run it. Once in the game, choose Multiplayer. Make sure the Connection field at the top states Internet, click on Search Server at the left bottom and it will start displaying all the online servers. My server is named [NL] Koen Zomers OpenTTD Server. It is both reachable over IPv4 as well as IPv6. If you can't find me in the list, you can also manually connect to openttd.koenzomers.nl.