So I thought it would be a good idea to start a topic about computer games that feel like ACKS, that way people without the ability to play with others can still engage with that type of play. So far, I like:
Eador: Genesis - The other Eador games might also be good, but the introduction of the Pilot class in one of the later versions of the game breaks immersion a bit. I can actually see a campaign based on the Eador world: limited magic, creatures, etcetera.
Sovereignty - More of a tactical simulation game, but the world is interesting and while magic is present its not incredibly invasive. Have often thought of creating a campaign based on the world presented in the game. Trade is a huge part of the campaign because certain trade goods are required for the production of various units.
Feel free to add to this list...
The old D&D game Birthright: The Gorgon's Alliance is probably what comes closest gameplay wise: kingdom management, RTS army battles and party based dungeon exploration.
https://www.youtube.com/watch?v=Au1cjndVAhw
I feel like Mount and Blade provides the most similar thematic feel, out of things I've played in the last decade or so. It basically covers the "Conqueror" stage of ACKS.
If you really want a turn-based experience, the Ilwinter games (Dominions, and Conquest of Elysium) are the closest thing mechanically to ACKS; Conquest of Elysium is a lighter game that covers the "Conqueror" stage, and Dominions is a crunchier game that covers the "King" stage.
Portions of ACKS work well as a sort of add-on for existing plot-light RPG modules from the classic era, if you're willing to play a hybrid computer and solitaire-PnP game.
For example, you can use the Gold Box Companion to edit save and character files from the old Gold Box games (Pool of Radiance, Curse of the Azure Bonds, etc), allowing you to transform the piles of extra useless gold you'll accumulate (especially in the first couple games) into crafted magical items. ACKS provides a way to figure out when you're "allowed" to subtract off a few thousand gold in exchange for giving a character a wand of fireballs, although you'll have to make reasonable estimates for the size of the markets in the cities you visit. This is the content that really belonged in those games all along, so it's hardly cheating in my view. SSI was forced to use the official treasure categories from 1e, even though the sinks for all that money couldn't be implemented using the technology of that era.
I haven't tried doing this with any more modern games, but I suspect with a bit of adjustment you could use them for NWN modules as well.