I think there are a lot of classic game systems that express numbers as combat, where it really could be anything else and still have the same type of gameplay. I've just started thinking about it, but I think I'll most likely go for some classic concept but transform it to not be about violence.
Might have another go at one of my favourites, tower defense, the genre itself really boils down to space/path management and number synergies.
Viewing post in Game Ideas (Brainstorm)
Haha, a marketplace was actually one of the things I was considering!
With both layout design to force a long walk, but also placing goods with synergies or sales. Maybe certain goods work better further along the park or just at the checkout, and some things like a sign or suggested recipe can make a customer walk backwards for a bit.
The endgame could be to make as much in sales as possible, with the classic "enemy health" being represented by a customers wallet / budget instead, and the goal being both to maximize total revenue as well as try to have no customers go through the store without buying anything.
It's probably the theme I like the most so far, other ones were traffic/shipping-based, but I like the sillyness of the store one :D
Though just reading through my description above I can already see the scope creep!