Teleporting, especially if it was possible to run with energy generated by renewables.

It would solve most if not all of the world's problems, human or otherwise.

- fossil fuel consumption would be almost null, thus a good deal of the air pollution would be gone, and the destruction of specific areas where fuel is gathered from would stop

- there would be no wars fought over said fuel

- no wars fought over water

- people in places where food is grown could receive fair pay for their work, since there would be virtually no middlemen between themselves and their final customer, plus no giant expenses due to transportation (this would apply to most products, really, not just food)

- food waste could decrease almost to zero since we would not produce more than we need to compensate the loss of a product due to short shelf life

- both fauna and flora would thrive and ecosystems would be rebalanced, since humans would not need to invade more wild territories to build roads, railways or crop fields

- family and friendship ties could become stronger, communities could become more personal and people would return to seeing their fellow human as an individual, not a number

- and other stuff I'm sure more people would point out and that I'm not thinking about right now...