In my mind, there are three alien technologies that would completely change humanity, assuming that there isn’t some enormous paradigm shift (e.g. we can have out-of-body-experiences i.e. OBEs like the ones described by Robert Monroe):
Free and unlimited energy (zero point energy) Atomic 3D printing. Like a replicator, this would imply a post-scarcity world. Robotic//Non-Human Labor Replacement. If you have a technology that will allow non-humans to perform labor for you, then you’ve freed yourself from working.
What do YOU think would be the most important/useful tech NHIs could provide?