Evan Williams did not want to start another start-up. He had already enjoyed the kind of rare, unfathomable success most entrepreneurs only dream of, starting tech companies that made products used by millions — the early blogging site Blogger, the social media giant Twitter, the publishing platform Medium.

Along the way, Mr. Williams had grappled with corporate turmoil and angst. His last company, Medium, was a decade-long slog that never lived up to its $600 million valuation or lofty mission of solving the internet’s ugliest problems. By the time he stepped down as chief executive in 2022, he had no desire to do it again, he said.

But he was lonely. He had gotten divorced and moved cross-country twice in a few years. Before his 50th birthday in 2022, he realized he had “underinvested” in his friendships, he said. Post-pandemic, he did not even know where many of his friends were living.

“I was doing a lot of reflecting,” Mr. Williams said. “In this stage of life, I really wanted to focus on relationships.”

Pouring so much energy into his start-ups was one reason he had this problem. But maybe a start-up could also help fix it.

In 2022, Mr. Williams began working on a Rolodex app that would tell him where his friends were living and traveling. It would be more “social” than “social media,” with none of the comments, stories, posts, likes, hearts or follows that made his previous creations so addicting.