Thursday, President Barack Obama was joined by many elected officials in New York City to celebrate and honor the completion of the September 11 Memorial and Museum in New York City. Obama began his speech about an unnamed man with a red handkerchief who, through smoke and fire, rescued dozens of people from the World Trade Center. A man who carried women down more than 70 flights of stairs just to go back up in search of more survivors. That man did not come back down as the tower collapsed.     

His story, and many of the brave men, women and children who died on 9/11, will be on display at the memorial. Before you visit, you can download the 9/11 Memorial Guide and the 9/11 Museum Audio apps to help you explore and hear more of their stories. The audio app, which was just released last week, features stories from 9/11 and the recovery of what would become Ground Zero. It also shares information on the museums archaeological elements and architectural designs of the memorial and museum.     

"All who come here will find it to be a profound and moving experience," Obama said Thursday. "Here, at this memorial, this museum, we come together. We stand in the footprint of two mighty towers, graced by the rush of eternal waters. We look into the faces of nearly 3,000 innocent souls.... we can touch their names and hear their voices and glimpse the small items that speak to the beauty of their lives; a wedding ring, a dusty helmet, a shining badge. Here we tell their story, so that generations yet unborn will never forget."     

The three audio guide tours on the app are Witnessing History, Discovering History and Building History.    

Witnessing History, narrated by award-winning actor Robert De Niro, chronicles 9/11 and its aftermath. In this tour users will hear about and from first responders, recover workers, family member of those killed on 9/11 and journalists.     

Discovering History, designed for children ages 8 - 11, focuses on the museum's artifacts and "provides an age-appropriate recounting of the events on 9/11.     

Building History features voice of recovery workers at Ground Zero, architect and preservationists describing the remnants of the World Trade Center that can be viewed in the Museum.     

You can watch the ceremony of the opening of the September 11 Memorial below. Both apps are currently available to download for free from the App Store or iTunes. The September 11 Memorial and Museum officially opens to the public May 21.