If unfamiliar, simutrans is a game very much like transport tycoon, it tends towards being more systems heavy than TTD and is generally considered more of a challenge.

Some of the difference from transport tycoon include factories have contracts with specific other factories, that is you can not just deliver iron ore to any steel mill, it has to be a specific one. goods can back up, when this happens quantities ordered will be reduced and your income can fall, you have to make sure the entire supply chain is handled before it backups up on you.

If trying it out for the first time an important thing to note is that the paksets are not just graphical changes but more like game code. that is, pak64 plays very different from pak128. I mostly play pak64 but I think to generalize pak64 tries to force you to optimize your running costs and pak128 you have to optimize your acquisition costs.

It is on steam, this might be the easiest way to play