A widely discussed topic in the past few years. Re-introduced substances utilized by Russian military, athletes, and bio-hackers (a term most prevalent in the Silicone Valley programers community).
In general, what nootropics do is increase oxygen flow to the brain, and as a result increase cognitive function, focus, and creativity, mitigate oxidative stress and reduce cellular stress levels.
Some also increase stamina and power, and reduce recovery time. Many may also promote healing of tissues, muscles and bones, and regeneration of nerves (neuroplasticity).
Many nootropics are lab synthesized substances (chemicals), which can also have side effects on the body such as mood swings, heart palpitations, insomnia, and adrenal fatigue, so there is a price in taking them.
There are several plants/herbs which are nootropics as well, and many can have no side-effects when taken in proper dosages, as well as have long-term beneficial effects on the cells and nervous system.