You probably have a lot of friends on Facebook, but chances are there are only a few people—and one in particular—that you interact with most in real life.

A new, free app called Pair wants to make it easier to connect with your special someone, whether it’s a significant other, family member, or friend. And while the app—which allows you to share messages, videos, and “kisses” with one other person—may sound a bit silly, it shows there’s still plenty of room for innovating in the increasingly crowded field for social mobile apps.

Stats indicate Pair may be on to something, too: In the first four days since it was released last Friday, it snagged more than 50,000 registered users, who sent over a million messages to each other. And while Pair was eligible for $150,000 in guaranteed funding since it participated in startup incubator Y Combinator’s just-completed winter session, it has also received funding from Dave Morin, CEO of another social mobile app, Path.

Pair began as something else entirely. Aswin Rajendiran, 27, says he and his four cofounders were initially working on software called Maide that could control 3-D CAD tools via the iPad. The founders, all of whom have graduated from or still attend Canada’s University of Waterloo, moved to Mountain View, California, several months ago to develop Maide at Y Combinator. But while they received good feedback for their project, “it wasn’t an everyday-use kind of thing,” Rajendiran says.

While brainstorming new ideas, they started thinking about the difficulty of keeping up communication in long-distance relationships—a problem three of them encountered as they worked to sustain relationships in the wake of the recent move to the United States.

Recognizing that we tend to communicate mostly with just one or two people, and that many of us use a number of methods to communicate with these folks, Rajendiran and his collaborators came up with Pair to simplify and amplify one-on-one connections.

Once you download Pair onto your iPhone (Rajendiran says an Android app will be available in about a week), you invite one other person to use the app with you. After they accept, Pair allows you to send each other messages, videos, photos, simple sketches, and more. There are several interactive features, too, including one called Thumbkiss, which shows a fingerprint when you press on the screen and makes both phones vibrate when you and your partner touch the same part of the display. To keep Pair communication private, the app can be locked with a four-digit code.

For Craig Elimeliah, the digital director at advertising agency RAPP in New York, Pair is like having a private version of Facebook or Twitter. He says he initially tried it because staying on top of new tech is part of his job, but quickly realized the app works well for sharing messages and links with his wife that their children won’t see when playing around with their parents’ phones. 

 “It’s kind of romantic,” he says. “There’s something about it where it’s just paired between her and I and there is nothing else on the screen. It keeps conversations focused.”

Rajendiran says that, for now, the focus is on improving the quality of interactions between users, rather than on making money. But the startup might eventually sell premium features, he says.

Catalina Toma, an assistant professor at the University of Wisconsin-Madison who studies the impact of technology on relationships, says Pair helps people let their partners know they’re important, which is key to keeping a close, happy connection.  

“I think close couples do this kind of behavior anyway—they do texting, send photos—and this app just brings them together in one platform and recognizes the importance of this behavior,” she says.

And Pair isn’t just bringing together significant others. James Tamplin, a Y Combinator alum and CEO of online chat software provider Envolve, has been playing around with the app with his cofounder and says he could see it becoming a tool even for those in nonromantic relationships.

“It’s got the hook, which is the relationship part, but ultimately it’s a rich messaging application,” he says. “I think they can use that technology to expand it beyond couples and have it be useful and productive.”