LiSE

LiSE 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. And if you don't want to write a user interface, you can play the game in the IDE.

The LiSE data model has been designed from the ground up to support debugging of complex simulations. 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.