LiSE

LiSE manages the rules and world state of your Maxis-style simulation.

Rules are snippets of Python code with simple effects, linked to other code determining when the rules should run. You can reapply rules to different parts of the world, or change when they run, without writing new code.

LiSE lets you time travel. It remembers everything that ever happened in the simulation, so that when something strange happens in a playtester's game, and they send you their save file, you can track down the cause, even if it happened long before the tester knew to look for it.

It's pronounced "lies". The screenshots are of ELiDE, the graphical development tool; LiSE itself is headless, and can be run as a server, though this isn't very well supported yet.

If you already have Python version 3.8 or later, you can install LiSE and ELiDE in your command line, with 

python -m pip install -U LiSE ELiDE

Then, run ELiDE like

python -m ELiDE

python3 -m pip install -U LiSE ELiDE

python3 -m ELiDE