iPad: It's been 10 years. No doubt you still vividly remember where you were on 9/11. If you want to reflect on the event at your own pace or visit the 9/11 Memorial virtually, this free app is an impressive experience.
Videos and images are usually more powerful than words, and that's very much so the case here. It's like holding a piece of history -- albeit, on an iPad -- in your hands. You can view footage of the Twin Towers while it was being constructed, in everyday use before 9/11, the awful day of the attacks, and progress on the memorial site since then.
While it's mostly an interactive documentary on the architectural and engineering aspects of the Twin Towers and the Memorial, there's a lot of unique and moving footage. The app is a way in to a very important and emotionally charged landmark (one you might not be able or want to visit at this point in time in real life).
The 911 Memorial: Past, Present and Future [iTunes App Store]