With the assistance, however, came problems getting the aid to the victims' families and others who suffered as a result of the attacks. Questions arose about accountability, as did worries that the already poor and needy would go without. A year later, the world of philanthropy is still struggling to absorb the changes.
"It's not as simple as saying, 'OK folks, let's all work together,'" said Suzanne Coffman at Guidestar, a nonprofit organization that monitors charities nationally. "It takes a long time to make institutional change."
The deluge of aid began immediately after the attacks. Barely two weeks later, donations hit $500 million.
The sources were amazingly diverse: school bake sales in Wyoming, Formula One drivers donating race helmets, an all-star concert at Madison Square Garden featuring Paul McCartney.
A report in June estimated private donors gave $1.88 billion for victims and their families. Other estimates ranged as high as $2.7 billion - and that's not counting the federal government's billions in direct aid and the victims' compensation fund.
The 10 largest charities told The Associated Press they have collected $2.3 billion and distributed $1.49 billion so far.
"Think of hurricanes that were huge - Andrew, down in Florida - we're talking hundreds of millions of dollars. But not at this magnitude," said Leo Arnoult, chairman of the American Association of Fund-raising Counsel in Indianapolis.
The needs were immediate, both for families of those killed and for those who lost homes, businesses and jobs. A pier on the Hudson River was transformed into a charity mall, offering immediate help with rent, food, counseling and more.
The assistance gave Mary Ellen Salamone, whose husband, John, died in the attacks, a way to answer her three young children's fears. "Look how good people are. Look how much good there is in the world," she told them.
A year later, some 67,000 people in the New York area have received aid. Families that lost someone received, on average, $90,000, though relatives of firefighters and police killed in the attacks - the focus of much fund-raising - generally received more than $1 million, charity officials estimated.
One big worry - that the massive Sept. 11 donations would hamper other charities - didn't prove true.
A June report estimated total 2001 giving at $212 billion, up slightly from the previous year. Sept. 11, which prompted the nation's biggest single burst of charity ever, accounted for barely 1 percent.
But getting the aid wasn't always simple in the chaos of the attacks' aftermath. Many complained of confusion and long waits.
"There's hardly anyone I've met who doesn't think this couldn't have been a smoother or easier process for them," said Robert Hurst, a Wall Street executive who oversaw coordination of some charity efforts in New York. "This was not easy."
Questions quickly surfaced. Who would decide how much a victim gets? How much of each gift would a charity spend before victims got help?
The Red Cross, the biggest single recipient of funds with $988 million so far, came in for the worst drubbing after officials acknowledged they were going to use some of the money received for other, non-Sept. 11 needs.
The charity forced out its president and changed course, declaring that all the money would go to the terror victims and their families.
"One of the lessons from September 11th is that the Red Cross must do a better job of educating donors about how we fund our disaster relief services, while honoring their intent," said David McLaughlin, the organization's chairman.
In New York, following the lead set by Oklahoma City after the 1995 bombing of the Murrah federal building, an umbrella group of major charities was set up to help manage the resources and the needs of victims.
Relying on a shared database, the 9/11 United Services Group focused on coordination and efficiency - though not without some rough-going, said Hurst, the chief executive. "There's not a natural inclination on the part of independent groups to share data and to naturally cooperate."
Hurst hopes lessons learned by his group can be shared by other charities and nonprofit organizations. Cooperation works better than competition; computer-coordinated tracking and delivery of aid can speed services and give the donating public more confidence, he said.
"This should be the wave of the future," Hurst said. "We can get there."