One of the biggest (and in my opinion best) simulation games out there is called ‘Transport Tycoon Deluxe’. This is an oldie, and was first published in 1994 by a company called ‘MicroPose’ by the name of ‘Transport Tycoon’. In 1996 it was republished with a polished gameplay and graphics, as ‘Transport Tycoon Deluxe’ and I play this version of the game even today 🙂
Its all about transport of goods and passengers from cities, plantations, mines, factories and so on, and it is easy to lose some hours in playing this game for sure 🙂 It is even multiplayer so you can play against a friend if ya wish.
This game is still so popular that an Open Source version of the game have been made, called ‘Open Transport Tycoon Deluxe’ and its freely downloadable through the https://www.openttd.org homesite. The OpenTTD features addons as a slightly better AI and huuuge maps, compared to the original game.
The original game is now also ‘Abandonware’ and should be easily found by using Google’s search function.
Edit: You can even find an Online version of this game (browser based) at http://epicport.com/en/ttd (Not tested this myself yet).