That's not a day I ever want to live through again. I grew up in NYC, now live about 50 miles north of it.
Sunday, my wife took my two boys (one 2 year old, the other two months) and dog down to the city to stay with the inlaws while I redid the floors that week. That morning, the only care I had in the world was that the Giants dropped the season opener to the Broncos the night before.
I was listening to WNYC that morning and heard a report that a small plane may have hit one of the towers. I had to reroute the cable and grab the TV from storage, by then the horror had unfolded. Got through to my wife for a second, she didn't know about it yet, but then the phone was out.
I have two brothers, one who worked a few blocks from the Trade Center, the other FDNY who was in Ten Truck, which was across the street from the Towers (and the only NYC firehouse that never reopened).
So, my entire family was in the thick of it and I was stuck here, no phone, Thruway closed so I couldn't go down there, staring at it all falling apart. Of course that was absolutely zero compared to what people were suffering through.
Edit: Both of my brothers survived. One was nearly crushed during a ferry evacuation and the other actually transferred to a different house beforehand (he was tired of walking up stairs during the multiple false alarms every week). He finished his shift and was on his way home when he saw the smoke, turned around and headed back to firehouse. The guys on duty left, but he was boarding a bus in gear when he was pulled off, ordered to stay at the house since a NJ company had to come in to cover the area and needed someone who to be a guide. So he sat and listened to it unfold on the FDNY radio while everyone he has known for 15 years died.