Orb.farm is a pixel-art glass bowl you can fill with water, sand, stone, wood, plankton, fish and other things useful for the creation of underwater ecologies. [via Hacker News]
This is a virtual ecosystem where different species of creature can live, grow and die as part of a self-contained food chain.
A fun way to approach such things is to imagine that we experience a multiversal cosmology and that everything you do in the simulation is lived in other universes, with all the moral and emotional consequences this implies.