The hottest technology trend is apps that let anyone share anything, which is why Grace Lichaa recently found a group of strangers eating her home-cooked macaroni.

Feastly Inc. sells dinners to people at the homes of various cooks. Danny Harris

About a dozen people she met through the Internet arrived, mostly on time, at her Washington, D.C., house in November for three flavors of macaroni and cheese: garlic-crusted, goat cheese tomato, and curried. Ms. Lichaa, 32 years old, advertised seats for the "mac attack" on a site called for $19.80 each.

Feastly asks diners to respect a "virtual Mom" at the gatherings. Mom is "cool with elbows on the table, but please respect the host," the company specifies online. Sharing wash-up duties is optional.

"Everybody was amazingly gracious," says Ms. Lichaa. Some diners even brought beer.

Dinners with strangers are just one front in what Internet companies and investors are dubbing the share economy: niche marketplaces for things that get cheaper when people use them together. Lately Internet startups have, in all earnestness, set up businesses to "share" pet care, wedding gowns, child rearing and more.

Got some lousy holiday presents? Re-gift them at, which describes itself as "a magical place where people share things with friends.", a San Francisco startup, matches dog owners with sitters, making for a unique pet experience.

Like leftovers? lets you cook and trade dishes with other moms.

Need a new dress? Try 99dresses Inc., an online marketplace where people sell their old dresses for "buttons," or virtual currency that allows them to buy more dresses from other users.

It could be ridiculous—or the next big thing. Avis Budget Group Inc. CAR +1.31% Avis Budget Group Inc. U.S.: Nasdaq $65.07 +0.84 +1.31% Dec. 26, 2014 4:00 pm Volume (Delayed 15m) : 845,087 AFTER HOURS $65.08 +0.01 +0.01% Dec. 26, 2014 4:44 pm Volume (Delayed 15m) : 11,674 P/E Ratio 34.74 Market Cap $6.82 Billion Dividend Yield N/A Rev. per Employee $291,310 11/06/14 The Morning Download: Avis Bud... 11/05/14 Avis Budget Shifts to Linux to... 10/30/14 Stocks to Watch: Wal-Mart, Tim... More quote details and news » this month agreed to acquire shared car provider Zipcar Inc. for about $500 million. Venture capitalists last fall valued the sharing economy's rising star—a service called Airbnb Inc. that lets people rent their homes, or rooms in their homes, to strangers—at $2.5 billion.

As startups describing themselves the "Airbnb for" whatever multiply, the question that fewer people are asking is what shouldn't be shared.

In San Francisco, Adolfo Foronda's family is testing the limits. They weren't ready for a full-time puppy, but don't mind borrowing one. So a few months ago, Mr. Foronda signed up to be a dog sitter on DogVacay Inc., a website matching dog owners with paid sitters for a fee.

"It's the Airbnb for dogs," Mr. Foronda says, adding that his 5-year-old daughter Sophia screamed for joy when he told her the family was getting "temporary dogs."

To help dog owners get comfortable with the arrangement, Mr. Foronda creates a blog for each pooch on its inaugural visit, and updates it with photos of their adventures. The blog for a smashed-nosed Pekingese named Goofy features him staring longingly at a distant pumpkin patch, and him looking regal in the passenger seat of Mr. Foronda's car.

For anxious dog owners, Mr. Foronda will email regular updates on their dog's health, in some cases including bowel movements.

The next frontier may be sharing kids. Family by Design matches people who aren't in a position to have a child on their own with others to share co-parenting responsibilities. Darren Spedale, 38, the website's founder, says he started the company in 2012 after realizing his own biological clock was ticking but he didn't have someone with whom to raise a child.

The recently launched site prompts members to submit copies of government-issued identification and fill out detailed profiles and compatibility surveys to "share with other prospective parents who they are and how they think about parenting," Mr. Spedale says.

So far, the site has attracted thousands of prospective parents, says Mr. Spedale, though he isn't yet aware of any matches among people agreeing to co-parent.

The idea of sharing with Internet strangers is beginning to seem less risky, says Rachel Botsman, an Australian consultant who wrote a book about the share economy called "What's Mine Is Yours." Airbnb's success proved people will share their largest asset, she says, opening "the dialogue around how strangers can be trusted in new ways."

The law isn't always certain of what to make of the sharing economy. Sharing food can be particularly touchy because of health and hygiene laws. "A lot of times, I have to tell them [startups] they are violating the law," says attorney Janelle Orsi, who created a practice around the business of sharing stuff about five years ago.

To make complete strangers comfortable with one another when they share, some startups are turning to software. When London-based entrepreneur Nicolas Brusson designed his ride-sharing startup, BlaBlaCar, he wanted to limit awkward interactions. So riders can now indicate how talkative they are, from "Bla" (quiet) to "BlaBlaBla" (chatty). "It was a joke initially," says Mr. Brusson of the company's name. "But people remember the BlaBla feature."

Some Internet sharers get more than they bargained for. Tracy DiNunzio rented out a room on Airbnb for the first time in May 2010 to a traveling musician, who kept extending his stay. About a month later, the two were engaged.

On Airbnb, her now-husband left a review for her Los Angeles rental that said she showed "true Californian hospitality."

When the sharing happens face-to-face, sometimes it helps spell out the rules of etiquette.

Seattle life coach Jillian Harrington has rented out a room on Airbnb nearly 250 times, earning enough cash to start her own business. But there was one wrinkle: too many couples having loud romantic encounters down the hall. Ms. Harrington added a notice to her page on the site. "Awkward to ask this but: no loud sex or porn videos while I am in the apartment."

Ms. Lichaa, who hosts Feastly meals in Washington, helps break the ice by asking participants to turn to somebody else and ask about a "joyful moment" in their day. "Most of them are strangers, but it is a super comfortable place," she says.

There's still the question of why she bothers. Feastly co-founder Noah Karesh says he hopes to "democratize dining" and turn chefs into "micro-entrepreneurs." Feastly says it advises chefs to be familiar with local laws, which vary, and vets cooks before it lets them host.

Ms. Lichaa says it isn't really about the money. Instead, "it is kind of like going to a bar and meeting somebody," she says.

She did have a serious conversation with her mom before signing up. "You know how I cook big meals for my friends a lot and don't get paid for it?" she remembers explaining. "Now I am going it advertise on this website and have people come and pay me."

"That sounds like a great idea," her mother said. "Please be safe."

Write to Geoffrey A. Fowler at

Corrections & Amplifications
Darren Spedale started his company, Family By Design, in 2012. An earlier version of this article incorrectly said he started his company this year.