I was at work. Only 1 computer had internet access (remember, this was 8 years ago). Normally, we didn't even have a TV at work. But someone was raffling one off in the lunchroom because they had just purcahsed it, and then won a bigger one in a school raffle. So got to see the news covering the events of the day unfolding.
Hardest part for me, since I did not know anyone there, were the debates going on in our office shortly after the seeing the footage. A bunch of civil/structural enginners amazed that a building could withstand a crash like that, but then quickly trying to figure out what would happen when the heat melted the steel on those top floors. Predicting the future isn't always as good as it sounds.