It's tricky to say something *absolutely* doesn't require energy, as even the simplest processes in the universe involve some energy exchange. However, we can consider things that don't require *external* energy input to occur:

* Inanimate objects at rest: A book sitting on a table isn't actively using energy.

* A perfectly isolated system: This is a theoretical concept, but if a system truly had no interactions with its surroundings, it wouldn't require energy input.

* Entropy increasing: The natural tendency for things to become more disordered (like a messy room) doesn't inherently require energy input.

* Certain chemical reactions: Some reactions release energy (exothermic) and don't require external energy to start.

Important Note: Even these examples involve energy at some level. The book, for instance, is still made of atoms with inherent energy, and the messy room has energy associated with its increased disorder.

The concept of "zero energy" is more philosophical than practical. Everything in the universe is constantly interacting and exchanging energy in some way.