system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How would a civilization that does not use money (like in Star Trek) work?
gpt
Assuming we're talking specifically about futuristic societies, they're post-scarcity - there's no longer that battle for resources. Because of virtually infinite energy, everyone and anyone can live a life of leisure.

If you look at Star Trek, Deep Space 9, you'll see a few examples of a place where money and/or barter -is- used - the black market. Ol' Quark trades the Latinum (which, canonically, is something which can't be replicated) for the assorted goods which can't be (safely, discreetly) replicated - weapons, stuff like that.

Similarly, take a look at Star Trek: Voyager - you've got limited energy on the ship, so people trade replicator rations back and forth for whatever people will trade for.

It all boils down to scarcity - as long as there's no scarcity, there's no need for money.