Apps Aiming for Sharing Within Boundaries SOME friends were gushing recently about a new mobile application called Pair, intended for people in a relationship. Initially, I didn't see the appeal of the app, which lets the two partners send messages and photos back and forth. The idea of adding another service to the daily routine of Twitter, Facebook and their ilk seemed exhausting. And wouldn't it be just as easy to exchange e-mails, text messages or, better yet, just flirt face to face? Curious, I tried it - even though I'm single. I recruited a friend to help me test it. And, after a few hours, the app started to grow on me. Something was thrilling about the secret little notes that Shaun, my temporary beau, and I sent to each other throughout the day. The secrecy was welcome. We weren't cluttering up anyone else's feeds on Twitter, and didn't have to worry about random high school friends seeing and commenting on our exchanges on Facebook. In addition, there were gestures distinct to the app. It let us share information about our locations, and to exchange doodles, to-do lists and virtual nudges - all conveying that "I'm thinking about you." The app highlights the best elements of social networking - the warm, fuzzy feeling of being connected to people you care about when you're physically nowhere near them. And it says it eliminates some of the worst - the worry about who can see the content you're posting and how they may interpret it. Apparently, venture capitalists also see the point: The company that developed Pair raised $4.2 million in seed funding from a group of early investors last month. Pair is arriving as many of us are looking to use the Web and our phones much as we always have, but outside of the very public arenas of the social Web. It's a natural evolution of social networking, especially as Facebook and Twitter have swelled. The combination of privacy and intimate sharing has never looked so good - provided that it can be achieved. A handful of start-ups are appealing to users who may be tired of the social spotlight but still enjoy the whimsy of apps. "We've spent the last decade struggling with this," said Andrea Matwyshyn, an assistant professor of legal studies and business ethics at the Wharton School of the University of Pennsylvania. Companies are trying to figure out the relationship of privacy to users while also trying to provide personalization and customization of their services. Even the largest social networking sites sense a rising tide of awareness about the need to protect delicate and personal information that is shared about users online. Last month, Twitter announced that it was introducing a "do not track" feature that lets users keep Twitter from collecting personal information as they move around the Web. The feature isn't perfect - it works only on third-party sites that agree to acknowledge it. "People can't always foresee or understand what could happen to their data," Professor Matwyshyn said. But they know they don't want it ending up in the wrong hands. Companies that do figure out how to embed privacy into a social service could gain a business and marketing advantage - positioning themselves as safer spaces to share and exchange information. "We should encourage Web and mobile services to lead with their privacy practices and let users vote with their feet," wrote Fred Wilson, a venture capitalist in New York, in a recent blog post. Mr. Wilson is an investor in Duck Duck Go, a search engine that says it doesn't keep track of a user's search history. Gabriel Weinberg, one of the creators of Duck Duck Go, says it has been able to carve out a niche audience despite the dominance of juggernauts like Google and Bing. Last month, the site performed 45 million searches, and Mr. Weinberg predicts that next month the figure will inch toward 50 million. "It's easy to think that no one cares about privacy because they still use all the services that keep track of them," Mr. Weinberg said. Switching from services like Google may be hard for people who are accustomed to them, or who rely on them for functions like e-mail as well as search. "If the switching costs are too high, users aren't willing to make the trade and that's not unreasonable," he said. But if there's a viable alternative, they're more willing to do it. Many online companies that have tried to build businesses around their assertions of ensuring greater privacy have struggled to get off the ground. Diaspora and Appleseed, for example, both tried to create private alternatives to Facebook, but have gained little popularity. The makers of Blackhole, an app that let people surf and post content to the Web anonymously, recently decided to throw in the towel on their plans and are developing a virtual assistant for e-mail instead. On the Web, privacy is easily promised yet often breached. "Start-ups sometimes use that as a differentiator, but quickly are willing to compromise it to gain users or if it doesn't help," said David Tisch, an angel investor and the managing director of the New York branch of TechStars, a start-up incubator. Mr. Tisch says services that promise more security and privacy don't always have the technical skill to ensure that they're safe - or can't always anticipate how someone might breach their sites or services. "Privacy is hard, technically, to accomplish with real security, and I think people aren't necessarily able to achieve this all the time," he said. But that hasn't stopped some start-ups and entrepreneurs from trying. A few interesting examples are emerging. They include: Snapchat, an app that lets people set a time limit on how long pictures and other materials they share are visible, so there can be less worry about a potentially embarrassing photo getting into the wrong hands; and KickSend, a new company from Y Combinator, a tech incubator in Silicon Valley, that lets people share files privately with friends. Of course, no one expects users to desert the mainstream social networks. But perhaps intimacy online and services that let people communicate, connect and exchange information through apps and services a bit removed from the public eye will become a welcome and powerful reprieve. "Entrepreneurs are experimenting with how to appeal to users who are privacy-conscious and benefit from that," Professor Matwyshyn said. In the meantime, Web users will be experimenting, too, sometimes cautiously, to make sure their private lives stay private.