I'm pretty sure the first "computer in a sandbox game" was Jong's computer in Dwarf Fortress, implemented in that game's fluid pressure mechanics, in early 2010

I'm pretty sure the first "computer in a sandbox game" was Jong's computer in Dwarf Fortress, implemented in that game's fluid pressure mechanics, in early 2010. That was certainly what inspired many others to add deliberately circuit-y things to their games that could be be used to build computers - most notably Minecraft's redstone and Terraria's wires. In theory all you need is a way to implement a nand gate, and really good simulation speed.