LiSE

LiSE is a game engine in the sense of RPG Maker or Ren'Py. It assumes that there are certain problems any designer of life simulators will have, and provides powerful tools specialized to those problems. Though you will still need to write some Python code for your game, it should only be the code that describes how your game's world works. If you don't want to worry about the data structure that represents the world, LiSE gives you one that will work. If you don't want to write a user interface, you can play the game in the IDE. And then again, if your game is similar enough to one that's been freely released, you can import rules from that one, and not write that code yourself, after all.

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.