Understanding science papers. Written learning. Rationality software. Modafinil. Is a wakefulness stimulant drug developed in the 1980s.
It is prescribed for narcolepsy but is widely used off-label for its stimulating effects and to deal with sleep deficits. As such, many believe it helps their cognitive performance & productivity. (However, comparing it to the fictional drug NZT in the 2011 movie Limitless is a gross exaggeration.) I would describe its advantages over other common stimulants as: more powerful and less addictive & tolerating than or khat; much longer-lasting than nicotine; less likely to alter mood or produce ‘tweaking’ behavior than or Vyvanse; and much more legal & with almost no side-effects compared to methamphetamine or cocaine.
On any specific aspect, there may be a stimulant superior to modafinil, but few stimulants come close to modafinil’s overall package of being a long-lasting, safe, effective, non-mood-altering, quasi-legal stimulant, and that is why it has become so popular.