"The kids just fell in love with it," Clarke said.
Mayor Nutter praised Mr. Stuart's contributions.
"Rob cared deeply about the city. He was a friend and a supporter, and I just feel terrible for his wife, Sarah, and the family," Nutter said.
Mr. Stuart was known as "the phone guy" because he carried what looked like an old-fashioned phone receiver, with a cord, in his shirt pocket. It was actually a device that he believed helped protect him from cellphone radiation.
One of Mr. Stuart's big skills was coming up with a new concept and getting others interested, said Sam Little, who succeeded Mr. Stuart as president of the Logan Square Neighborhood Association.
"He was like an idea merchant," Little said.
Phil Goldsmith, a former city managing director, worked with Mr. Stuart at CeasefirePA, which aims to reduce trafficking in illegal guns. He praised Mr. Stuart's foresight and passion.
"He was a tireless and optimistic social entrepreneur," Goldsmith said. "I didn't always understand his ideas, but I always knew it was something to make the city a better place to live."
Mr. Stuart was best known for persuading railroad company CSX Corp. to allow public crossings into Schuylkill River Park at Race and Locust Streets. Beginning in 2003, he waged a four-year battle to allow those crossings, using the Internet and other technology to marshal support.
"We knew that as soon as the park was built that hundreds of thousands of people would want to use it and that not having that public access was ludicrous," said his wife, Sarah Clark-Stuart, who worked with her husband on that and many other issues.
Joseph Syrnick, president of the Schuylkill River Development Corp., said Mr. Stuart's classy tactics won people over.
"They weren't rabble-rousers. They weren't suing," he said. "They just got a lot of people together, worked nights and weekends, and wore the railroad down, and we're all going to benefit from it for the rest of our lives."
Mr. Stuart made a documentary about his efforts, Free the River Park, which he hoped other groups could use as a teaching tool.
He was born in Summit, N.J., but grew up in Morristown. As a high school student, he organized a debate that featured an appearance by 1980 third-party presidential candidate John Anderson.
"He understood the power of change and the power of making an impact, and he always wanted to set a high standard for doing that in whatever he pursued," Clark-Stuart said.
Mr. Stuart graduated from Rutgers University with honors and a degree in political science. After several years working for the New Jersey and Vermont Public Interest Research Groups, he moved to Philadelphia in 1995 when his wife got a job here. He did technology and political consulting for various companies before founding his communications firm, Evolve Strategies, in 2006.
In addition to his wife, Mr. Stuart is survived by their two daughters, Marina, 17, and Amelia, 13; his parents; a sister; and a brother.
The family plans a memorial service for 3 p.m. Saturday, Nov. 12, at Trinity Memorial Church, 22d and Spruce Streets.
In lieu of flowers, donations can be sent to benefit a community garden that Mr. Stuart helped found: Logan Square Garden Fund at Evolve Foundation, 1 S. Broad St., Suite 1840, Philadelphia 19107.
Contact staff writer Miriam Hill at 215-854-5520, email@example.com, or @miriamhill on Twitter.