Fatto generale: 1999 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1999 is the smallest number whose digits add to 28.
Trivia: 1999 is an unremarkable number.
Data storica: June 21st is the day in 1788 that New Hampshire ratifies the Constitution of the United States and is admitted as the 9th state in the United States.