Among Ripples is a free to play ecosystem management simulation game developed by Eat Create Sleep. In the game you manage a pond's ecosystem while experimenting with what you can do to find out what happens.
"In Among Ripples you are presented to a soothing and meditative experience where you can experiment at your leisure. As the caretaker of a small pond you decide which creatures should be introduced into the ecosystem, and what species will thrive. Study the creatures you introduce and learn more about them in order to shape a pond that you find sustainable. This game is a short but sweet experience where you get the opportunity to relax and think about the balance in nature."
Mac OS X 10.6 Snow Leopard or newer
Intel 1.6Ghz processor or faster
1 GB Memory
256 MB graphics memory
250 MB available hard disk space
Free download at steampowered.com