Inc.'s 11th annual 30 Under 30 list features the young founders taking on some of the world's biggest challenges. Here, meet On Second Thought.

Maci Peterson's ex-boyfriend kept calling, but she never seemed to be in the right place to answer the phone. She sent him a text.

"Hey, sorry, I keep missing your calls," she wrote.

Except, the text didn't come out saying "calls." It said something that rhymes with calls, something that starts with a "b," something you probably wouldn't want to say to your ex.

"Like everyone else, I started slamming my fingers against the phone," she says. She sent another text: "calls*." Then she got to thinking--what if there were a way to take that text back? She asked her friends--would they use an app that allowed them to do that? They said yeah.

The idea became the germ for On Second Thought, an app that lets you set a delay of up to a minute on each text, allowing you to swipe the text back and interrupt sending it in case you have second thoughts about what you're about to say. Users can also set a curfew that will hold texts until the next morning. (Pretty useful if you tend to text while drunk.) 

Since launching in 2014, On Second Thought has run mostly on funding from friends, family, and competitions, and is in the process of concluding a seed round. The app is currently available on Android and has 67,000 users spread throughout 200 countries.

Peterson started On Second Thought by the seat of her pants while still based in Washington, D.C., though she didn't come into the startup world without business experience. From 2009 to 2011, she ran Mwari, a magazine she started in 2006 as an undergraduate at Chapman University in Orange, California. Mwari, which means "young woman" in Swahili, was aimed at women of the African diaspora aged 18 to 24. Peterson also worked as an account executive at Washington Life Magazine , atThe Washington Post-owned African American culture online magazine The Root, and as a brand manager at Marriott.

It was in 2014 that she queried friends on their interest in retracting texts. She decided--more or less at the last minute--to take her idea to the Startup Oasis pitch competition at the South by Southwest Festival. But it wasn't as simple as deciding to go, she soon discovered.

Peterson booked a flight to Atlanta, where she planned to make a connection for a flight to Austin. She flew on a buddy pass through a family friend who worked for an airline. Upon arrival in Atlanta, she discovered connections to Austin were clogged with passengers headed to South by Southwest, many of whom were stuck in Atlanta after missing connections or dealing with delays.

"I realized I just needed to get in the vicinity of Austin," she says. She met a girl in Atlanta who was also looking to get to Austin, and the two agreed to fly to Houston where they split a rental car.

Peterson end?ed up hitchhiking part of the way to the pitch competition, because she was unable to get a taxi or Uber from the corporate park area of Austin where she was staying with a friend. She had completed her pitch deck and filed a provisional patent that morning. She placed first in the competition.

Mary Bush, who has a background in finance and sits on On Second Thought's advisory board, says she invested in the company because she thought the idea of an app that lets you unsend texts could work but also because she trusted Peterson's capabilities as a leader.

"If this can work, she's going to make it work," she says of Peterson, whom she describes as a hard worker, persistent and thorough, and inclusive in her leadership style. "I would say that she listens to others, but when a decision has to be taken she makes a decision."

Peterson attributes the successes of On Second Thought to hard work, but also to faith. Describing herself as a "regular old Jesus lover," she says "being an entrepreneur is really hard. I don't think anyone will say that it's a cakewalk. It's also a path where you have really, really high highs, and really, really low lows."

Peterson arrived in the Bay Area in the fall of 2015 after running On Second Thought for a time in Washington, D.C. She says she's run into challenges that have forced her to rethink the direction of the app. Faith helps her through rough patches. "It grounds me," she says.

Fundraising, for example, has been a challenge.  She ended up having to delay On Second Thought's seed round, originally slated for completion in September. "Raising money is a really tough process. You know you have to go through a lot of nos before you get to that yes," she says. While she won't divulge details at this time, she says some meetings with investors have inspired her to expand the app in new directions. 

She mentions that she's also had encounters that cause her to question whether investors express biases toward her as a black woman. She said one investor commented that she seemed too confident--something Peterson thinks a white male founder would be less likely to hear. "If I wasn't confident, they'd say, 'Oh she doesn't know her stuff.'" 

The next step for On Second Thought is international expansion. The company has been in talks with a Latin American cell carrier to start pre-loading the app, translated into Spanish and Portuguese, on phones following a release of a new version of the app late summer.  Pre-loads are slated to take place in batches of five to 10 million phones at a time. Peterson says she cannot yet disclose the name of the carrier.

The ultimate goal with international expansion is to offer payments processing and e-commerce opportunities through the app in markets where payments are often made by phone.

The messaging aspects of the app are great, says Peterson, but "I think where we really hit our meaning is when we start building features that will matter to people" in developing countries where banking systems are more fragmented and less accessible. "Really, it's just about the inclusivity." 

Will Yakowicz contributed reporting to this story.