NZT is a fictional compound in a movie called limitless, basically it's a brain booster, it gives access to more simultaneous neuron activity. are there any real cognitive enhancers out there?
As others have said, this compound is fictional. Leaving illegal compounds aside, I would vote for nootropics. And from them I find pramiracetam to be the best fit. I have found its action to be rather similar to the one described in the movie, although with no side effects. One of the most notable mechanisms of it is the highly selective potentiation of acetylcholine and improvement of brain blood flow. Papers on this chemical are easily accessible through Google, so I won't provide lnks.
However, no cognitive enhancers will do any good without proper motivation and conscious efforts. It is pointless to eat pills and hope that something will come and change who you are for the good. Cognitive enhancers need something baseline to enhance.
Looks like this question really belongs to CogSci SE, but I feel that I should complement this answer with some more information that is important to take into account.
Cognition/mind enhancement can be a double-edged sword for some people. Instead of giving pleasure directly, it actually enhances mind and calls for much more self-discipline and responsibility. For example, I practice meditation and some other mental disciplines for a long time already, and it came in handy to control and direct my mind. However, some people who tried pramiracetam reported that the intensity of their own mind was too much for them, they simply did not know what to do with it for they had no real task, motivation or big plan formed before administering the compound, and it could happen that they got themselves overwhelmed by many long-forgotten memories that rejuvinated in all their lucidity at the same time when the present day reality became much more integral and whole, without many pieces comfortably forgotten.
These memories could not necessarily be negative, but what about a super-fine image of the wallpapers pattern you were looking at when you were 3 years old, standing as bright as a day before your eyes when you try to sleep, eat or mate? And I am not even saying about the fact that recent events are perceived in much greater detail and integrity, senses sharpened greatly... Personally I was able to control my mind because I also practice it in daily life (without the enhancers), but this may not be easy for people who are not used to that.
Another issue such an enhanced mind could face is that people around remain as they are. The perceived difference can render them much less intelligent and almost dumb. A person with an "enhanced" cognition can find himself living in a world of dense people. This is in no way an offense, a similar condition can be observed when one with a body "enhanced" by a stimulant can run 3 miles and still feel not even slightly tired, while an average untrained person will extinguish in under a mile. It is true that there are lots of smart people in this world, but one has to be ready for a sudden shift of perception that could occur. I remember reading reports of piracetam users who say that while they became more effective in integrating knowledge, people around did not, and situations occured when "obvious" things were not immediately understood by the surrounding people which caused irritation and conflicts. One has to be careful as this may lead to social disadaptation.
This again calls for discipline, ability to love and appreciate other people, and actually rises many unusual ethical questions. As with any gain, one must always remember that love and understanding are essential.
Another example of a two-fold effect is piracetam - an older, less potent but nevertheless useful nootropic. While it has an effect which may with high probability result in enhanced cognition, it also rises agression due to stimulating the secretion of the thyroid gland. So again, this calls for enhanced discipline. (do not mix the terms "piracetam" and "pramiracetam" in this text, they mean different compounds).
In any way, it is always important to apply conscious approach to your own behavior and thinking, be it with or without enhancers. But with enhancers, the responsibility is times greater.
One more point to notice. While nootropics do not exhaust body in any way (they are not stimulants), it is very important to provide oneself with sufficient nutrition and sleep, and avoid drug usage such as nicotine, alcohol and other psychoactive drugs. Failing on any of that may significantly reduce the useful effect and in case with illicit drugs cause unpredictable consequences. Dietary supplements such as omega-3, lecitine, vitamins can also provide some support.
Disclaimer: aside from compiling information available online, what I am saying is also supported by personal experiences of 2 courses each 6 months long, taken with a pause of 1.5 years between them, 600mg pramiracetam 2 times a day. I don't smoke or drink alcohol. Both times the experience was life-altering.
Yes there are a few out there, though the mechanism is quite different to the film. Things that increase the activity of dopamine and norepinephrine particularly in the prefrontal cortex where a lot of your higher functions like decision making seem to be. Things that do this can include amphetamines (ritalin and other adhd medications) along with things like modafinil.