People literally have shared a ton of secrets with Frank Warren. Ten years ago, the Germantown, Md., resident launched a “community art project” with the goal of collecting 365 postcards bearing anonymous senders’ artfully depicted secrets. He got a bunch and started sharing them on a blog, PostSecret.com.

A phenomenon was born: Warren has received more than a million postcards, many of which appear on the popular PostSecret site, which boasts about 700 million visits. The project has spawned several books; a now-defunct app; an album of secrets read aloud; and a series of live events and museum exhibitions, including one at the American Visionary Art Museum in Baltimore. There, Warren’s now retired mail carrier, Kathy, was awarded a tiara that reads, “USPS Wonder Woman.” Here’s hoping it came with a box of Doan’s.

You’ll meet Kathy and a few others touched by PostSecret in Warren’s new book, “The World of PostSecret.” Filled with anonymous and often beautiful postcards that share people’s confessions and hopes, the book forms a vivid and intimate mosaic of 21st-century interior life.

It often looks pretty tragic. One postcard features a black-and-white photo of the Arc de Triomphe. “My mom is the reason I don’t kill myself,” it says. “And I know I am her reason, too. We have never said it, but I know we both know it’s true.” The PostSecret community has responded to these cries for help, raising $1 million over the years for HopeLine, the suicide awareness and prevention group.

The book’s other dark themes include addiction and loss. “To: The creators of Vicoden,” one person writes, “could I please spend Mother’s Day with your mom this year? You stole mine.” In another, soldiers bear a flag-draped coffin away from a plane. “I should have died instead of you,” it says. “I’m sorry.”

"The World of PostSecret" by Frank Warren. (William Morrow)

But “The World of PostSecret” isn’t all gloom. One submission depicts a man dressed as Santa Claus. “This is my dad,” it reads. “I dressed up as an elf & went around to hospitals passing out candy canes to ppl who won’t be home for Xmas. Our secret? We’re Jewish! Happy holidays PS!!”

Most pieces featured in the book tend to be meticulously crafted and earnest. But the most memorable, and often the funniest, are simple and frank. “I’m an athiest (sic) who prays regularly but only for soccer results” is scribbled over an image of a footballer. Another reads, “My kid is a drag. There I said it,” in purple ink on an otherwise blank white index card. “I wear flowery scents to keep my annoying, bossy, allergic coworker away from me,” reads another “(and she thinks she’s passive-aggressive).”

Warren says this, his sixth PostSecret book, may be his last. “Even though I still get excited each time I walk to my mailbox to check for secrets,” he writes, “I feel as if it might be time for a change.”

But even if he did leave PostSecret, this vibrant and active community, built on trust and empathy, probably would endure. (Warren says he plans to launch a new PostSecret app this winter.) “Secrets can make us feel isolated,” he writes, “but sometimes it just takes one person telling their truth to shatter the illusion that we are alone.”

Wilwol is a writer in Washington.

THE WORLD OF POSTSECRET

By Frank Warren

Morrow. 287 pp. $29.99