system
Given the following post, respond as if you're commenting on Reddit:
human
[General] What are some criminally ignored in-universe applications of your favourite SciFi tech that would be way more powerful than their signature ones?

For example, the Mass Effect from the ME saga. If used to sufficiently increase the mass of a bunch of Hydrogen gas, the protons of their molecules would start fusing at room temperature, regardless of the size of the reactor, (Cold Fusion similar to Muon catalized Fusion). This could be used to generate energy or to manufacture  elements on demand from available ones. This two things combined would almost make any civilization that had both a post scarcity one.

Also would allow to make miniature artificial stars to terraform whatever barren or frozen world you stumble upon.

With this 3 thing combined the ME races should be way on their way to K-III status, not some Kardashev-I with interstellar travel.
gpt
Star Trek is full of these. There are basic ones like how they ridiculously underutilize AI and replicators, but the one-off episodes are more fun.

There is one episode where they encounter a planet where people can't die, as long as they stay there. It's used as a prison. Not the homeworld of a utopian society of gods, a prison.

Then there's that one where they can make someone experience an entire simulated lifetime in a few minutes. This too could be used as a kind of immortality, or at least extending your experienced lifetime a millionfold. Or just imagine getting an entire education in a few seconds. The possibilities are endless. Instead, it's also used as a prison.