For location:
* "fuori" (outside)
* "dentro" (inside) - this is more specific than "fuori" and means the opposite of "outside"
* "sopra" (above)
* "sotto" (below)
For time:
* "fuori" (outside) can also be used to mean "outside of a certain time frame"
* "prima" (before)
* "dopo" (after)
For other contexts:
* "senza" (without) - opposite of "con" (with)
* "non" (not) - opposite of "si" (yes)
Examples:
* "Sono in casa" (I am at home) - "Sono fuori casa" (I am outside of the house)
* "Il libro è in biblioteca" (The book is in the library) - "Il libro non è in biblioteca" (The book is not in the library)
* "Arriva alle 3" (He arrives at 3) - "Arriva dopo le 3" (He arrives after 3)
It's important to consider the specific context when choosing the opposite of "in" in Italian.