Three years ago, Ernestine Fu was sitting at the iconic Philz coffee shop in Palo Alto studying for her Stanford exams. She tweeted about it, wondering if any of her friends were studying nearby. A few minutes later a stranger who had seen the tweet interrupted her to pitch his company. Talking about it years later, it’s clear this interruption was a turning point for Fu, as she explains how it changed her perceptions of social media from fun and personal to a public forum. Today, Fu and her team have launched HelloWorld as the first product out of Y Combinator’s hackathon, YC Hacks. The core idea of the app is a very simple way of answering "Where are you? What are you doing?" with text, maybe a picture, and your location. Posts stick around for 24 hours so your friends can see where you are and where you've been recently, then they disappear. “It’s both the very first program you write when you learn a new language,” Fu says, describing HelloWorld. “As well as a direct description of what the product does—it let’s you say hello to the world, your own personal world of friends.” Below, you can see a feed of your friends' latest updates filtered by location on the left; on the right, you can see one friends' updates in reverse chronological order. Friends can see how far away you are, but not your exact location, making the location aspect more similar to Secret than Foursquare. Users can ping each other with a push notification if they want a specific friend to know they're close by, or at their favorite brunch spot. The team behind HelloWorld talks a lot about location as a way to pleasantly surprise your friends, and they’re on to something there. It feels a bit like an early Twitter, where people are just quickly sharing what they're doing and what they're up to with a small group of friends. With ephemeral posts and posts that show how far your friends are but not their precise location, the team hopes HelloWorld can create an environment in which people are more willing to share their location. But perhaps the most compelling aspect of HelloWorld is the team behind it. Fu, who leads the team, graced the cover of Forbes three years ago under the headline, “All Star Student Entrepreneurs.” She has worked as an associate for Alsop Louie Partners since her sophomore year at Stanford, where she has earned two degrees and is currently a PhD candidate in engineering. She also co-authored a public service book with the former dean of the Stanford law school. “If she decides to become an entrepreneur,” said Tom Kosnik, an engineering and entrepreneurship professor at Stanford in Forbes’ 2011 story on Fu, “she’s going to come up with something that will astonish us all.” Joining her are Michael Carter, Max Goodman, Jeff Himmelman, and David Li. Carter was recognized by the World Wide Web Consortium (W3C) for designing the first WebSocket protocol. Goodman got a CS degree in his teens and wrote Reddit’s first browser plugin. Himmelman is a former artist at Warner Brother Games, where he worked on titles like Wizards of the Cost, Dominion, and Fantasy Flight. Li worked on the framework for several teams within Google, including Google+. The team hasn’t raised any funding yet, noting they want to get the product out to users first. HelloWorld is available for download on iOS and Android now. Use the password "techcrunch" to download the iOS version.