Cellscape

Cellscape puts you in the role of a little microbe trying to survive and increase the population of your species. You start out in a tiny patch of soil that was recently disturbed, so the habitat is pretty much gone. It's just a bunch of loose mineral particles and some bacteria. You start swimming around eating bacteria, and each time you eat one, you grow a little bit. Once you've grown enough, you divide and produce a little copy of yourself which swims off on its own while you continue eating and dividing.

In the meantime, the environment around you is changing. Bacteria change the physical structure of the soil, pushing particles together to create new obstacles that can block your way or save you from predators. Bacteria also start to diversify, with different types causing different effects when you eat them (eg. extra growth or a speed boost). Other types of microbes start showing up and competing with you for food, and soon all this activity has attracted predators. Some predators are passive and you just need to stay out of their way, while others will actively chase. You'll also start to see other kinds of hazards like a Heliozoan that stuns you on contact, biofilms with various buffs and debuffs, and even viruses you can use against predators.

Survive for as long as you can in a living, changing, and increasingly complex ecosystem.