My father and I were on a plane that was later discovered to have box cutters on it (like one's used by the hijackers). You can read about it in the 9-11 Report(!). We were told via announcement that a plan had hit the World Trade Centre and that the FAA had grounded all aircraft in the US.
My sister was due to have an internship at a company in the twin towers starting that Jan. She lived in Lower Manhattan.
My mum was a flight attendant and normally flew similar routes as those involved...
But we were lucky... Others weren't. It was a sh*t day.