At first glance, a screensharing app might not seem to have much of a coolness factor.

But Firefly is a simple solution to what has been a pretty complicated problem: How do you show someone in another location exactly what you're seeing on your computer screen? Other solutions out there, such as Cisco's WebEx or GoToMeeting, can get the job done but they require clunky downloads to do it. Firefly is lightweight--meaning, no downloads, browser plugins, or Java required--and it works on any device.

It sounds like the kind of idea you might expect from someone who's worked in a big company for a long time and been frustrated with using corporate-manded software.

But this particular app came from three 20-somethings at the University of Pennsylvania. Co-founder Dan Shipper was talking to his dad when the elder Shipper explained that he really need a very simple screensharing solution. "When you're on an Excel spreadsheet and you say 'E5,' everyone knows what you're talking about," Shipper says. "He wanted something like that for websites."

So Shipper's two co-founders, Patrick Leahy and Justin Meltzer, coded the app at the PennApps student hackathon on campus in January 2012 and wound up winning a prize for it. At yet another hackathon a couple months later, Shipper says, they rebuilt it in 36 hours using a different coding language, and caught the eye of several larger companies in attendance.

That summer they put $3,000 of their own savings into a bank account and set to work incorporating some of the feedback they had received and finding beta testers.

They officially launched Firefly in September and quickly garnered favorable press from tech websites.

It would be an understatement to say these young entrepreneurs have given some thought to the best way to build a start-up. Firefly isn't even their first venture: They built Airtime, an app for managing marketing messages in email signatures, the year before. (The app now makes the trio about $300 to $400 a month.)

"With Airtime, we talked to customers and got a good sense that it was valuable but then we built it without customer feedback," Shipper says. "But with Firefly we took a different approach: We're always talking to customers. The product is exactly fitted to the people who use it." They know exactly who those people are, by the way. "Small- to medium-sized SaaS [software-as-a-service] businesses with at least one dedicated customer service rep who does does phone or Web support," Shipper says.

And what about how to make money? These founders have been earning revenue since they started. Firefly's service ranges from $15 to $60 a month. They have about 50 paying customers and a couple hundred free customers.

They also have pretty staunch views on why entrepreneurs shouldn't raise VC money.

"Raising money adds a lot of extra pressure and doesn't allow you to learn and grow organically as you build a business from the ground up," says Shipper, a philosophy major in his junior year. He and Leahy, who's a senior studying entrepreneurship and Chinese, are firmly committed to earning their college degrees before they become full-time entrepreneurs--even though Shipper already has received some very public job offers; Meltzer has already earned a degree in entrepreneurship and finance from Penn.

Firefly did receive $20,000 in the form of a convertible note from the Dorm Room Fund, a student-run investment fund within the Philadelphia-based VC firm First Round Capital. But Shipper calls it "enough money to experiment" but still stay scrappy.

Derek Kleinow, a second-year MBA student at Penn's Wharton School of Business and one of Dorm Room's members, sees a very bright future for the Firefly team. "If you had asked me a year ago about screensharing, I would have yawned," he says. "But they found a way to make a product a lot better. That fresh thinking could be applied to a lot of areas. I have no idea what they'll come up with next but I know it will be awesome."