My favourite is AirWay Sim [0], a massively-multiplayer online airline simulation. Incredibly detailed business sim financially — with full financial statement generation - as well as operationally. One must decide on hubs, airplane types, fuel hedging, scheduling.. the list is endless.
I’ve spent a non-trivial portion of my free time in university building airlines in this game. Highly recommended.
I'll refer one that I don't see mentioned very often, that is my favorite business simulation game: Capitalism / Capitalism Lab (latest version). It has been around for about 25 years, the author keeps working on the concept.
This is a really amazing sim, and I'm surprised how under-the-radar it is. It's kind of Dwarf-Fortress-esque in how it has this slightly antiquated presentation, but hiding behind it is an incredibly deep sim, where the author keeps on adding new features.
I asked a similar question on the previous thread about SimRefinery. For my criterion of a ‘more serious’ simulation, the answers were Capsim and Capitalism Plus.
I’ve spent a non-trivial portion of my free time in university building airlines in this game. Highly recommended.
[0] https://www.airwaysim.com/