Sandra Sukstorf had only recently watched her husband cross the finish line of the Boston Marathon when she heard the explosion.

From her vantage point in a hotel room overlooking the last block of the route, she saw the windows blow out of storefronts on the street below. She watched blood splatter the sidewalks where proud friends and family had stood only moments before. And even as she ran from the window to shelter in the hotel stairwell, she glimpsed neon-jacketed emergency responders tearing down fences —“like Hercules” -- to get to the wounded.

It was not Sukstorf’s last glimpse of Bostonian heroism. As she and her husband wandered the streets, he so exhausted he could barely walk down the stairs, another hotel opened its lobby to the tired runners. When they couldn’t get back to their room, Sukstorf posted a message online and, within half an hour, heard from more than 200 strangers offering a ride or a place to stay.

Each message was a reminder of humanity in the midst of an inhuman tragedy. And even as the smoke from Monday’s bomb blasts cleared, Boston saw many such reminders.

“People were so extraordinary,” Sukstorf said. “You could never, ever prepare for something like this, but they did everything they could.”

Much of the outpouring found a home in the crowdsourced Google form where Sukstorf first posted her request for housing. The form, set up by the Boston Globe’s digital team, collected the e-mail addresses and phone numbers of stranded marathoners and Bostonians with guest rooms or couches to spare. More than 80 people offered housing within the first minute, according to the Guardian. By Tuesdaymorning, several thousand people had opened up their homes.

Eli Akerstein, who lives only six blocks from the finish line, posted within minutes.

“The neighborhood actually feels pretty normal now, but a lot of people can’t get into their hotels,” he said by phone Monday night, about three hours after the blasts. He hung up abruptly when he got another call from an unknown number.

“Sorry, it could be someone,” he said, meaning someone who needed help.

Similar offers of food, housing and company blanketed Twitter and Couchsurfing, a site that typically connects locals to adventurous travelers. Ramsey Mohsen and his girlfriend Ali Hatfield, a marathoner from Kansas City, Mo., spent an hour eating crackers and drinking beers in a stranger’s living room after she saw them shivering on the street, unable to get back to their Copley Square hotel.

Boston Globe reporter Chelsea Conaboy said she encountered Lutheran ministers walking down Commonwealth Avenue with Bibles for those who needed them, while a group of Christian chaplains affiliated with the Occupy movement promised “water and a hymnal” to shaken witnesses.

El Pelon Taqueria, a Mexican restaurant with locations in Boston’s Fenway and Brighton neighborhoods, promised free Wifi, outlets, food and drinks to people who needed it. Owner Jose Torres said on Twitter that he was only repaying the kindness Boston showed him in 2007 and 2009, when his restaurants burned down twice in electrical fires.

“My coworkers + staff deserve a lot of credit,” Torres wrote, “not one blinked when ask[ed], not one [went] home when they could, those not working came in.”

In a statement Tuesday morning, President Obama thanked the Bostonians who responded “selflessly” and “compassionately” to the attacks. But for people like Kenneth Rahn, who offered to pick up stranded marathoners and host them in his Providence, R.I. home, an hour’s drive away, there was no other choice.

“It impacts us too, even outside of Boston,” Rahn said. “It’s the least I can do.”

After a beat, he added: “Really, it’s the only thing I can do.”