WASHINGTON — Everything about the online world encourages sharing — share your recent purchase on Amazon, share your dining experience on Yelp, share your thoughts about Beyoncé on Twitter. But what about the things you would rather not share with everyone in your social network, such as the cheesy pet name you call your boyfriend or the startlingly high number of romantic comedies your wife forced you to watch on Netflix last month?

There is an app for that. In the past year, several "couples apps" — with names like Duet, Avocado and Couple — have come to market, promising to "bring the romance back to one-on-one messaging" by creating a social network of two. One leader in the market, Between, launched in South Korea last year and has already been downloaded 1 million times. Anyone who has endured watching couples shamelessly canoodle on Facebook or Twitter should be relieved. These apps promise to do for digital intimacy what the automobile did for analog couples in the 20th century — create opportunities for on-the-go private interactions in an otherwise transparent world. Like the road to true love, the apps that offer to track it do not always run smoothly.

Couples apps are part of a movement away from promiscuous sharing online to sharing more exclusively. Like Glassboard, a social network for small groups that positions itself as an alternative to Facebook, couples apps emphasize privacy, intimacy and the need to humanize our digital interactions by scaling them down. In the two-person domain of the couples app, no one will stumble across pictures of ex-boyfriends or ex-girlfriends. Sappy messages, flirty texts, and risqué pictures remain safe from the prying eyes of employers or judgmental relatives.

But reimagining the online world as an intimate space can be a tough sell, as Facebook discovered last year when it made intimate sharing compulsive by generating "couples pages" for its users. The pages, whose privacy settings can be tweaked but which cannot be deleted, display everything posted or tagged on Facebook by you and the person you have designated as your significant other. Not all users were happy to see their romantic partnerships curated by Facebook's algorithms. ("I want to vomit," one blogger wrote.)

Couples apps have taken several different approaches for marketing their services. Avocado emphasizes convenience by combining many of the ways we already communicate with our partners — text, email, chat, video — into a single app with additional features such as a "send your mood" button and templates for shared lists and photos.

Other apps emphasize the creation and storing of romantic memories and experiences. Couple (an app company formed from the recent merger of U.K.-based private sharing app Cupple and U.S.-based app Pair) offers the opportunity for mutual real-time doodling on smartphone screens as well as a cloying feature called "thumb-kiss," in which each person places his or her fingerprint on the smartphone screen so that, once aligned, both screens glow red while the phone vibrates suggestively.

All of these couples apps market themselves as technologies for enhancing authentic romantic experience. An advertisement for the app Duet shows unbelievably adorable pairs of people dancing, eating meals outside by candlelight, picnicking, playing chess and tandem bicycle-riding. In the final image, a man and woman perched on an orange scooter and wearing their wedding clothes, zoom off to their ostensibly happy ending. It is worth noting that not a single image of a smartphone (or any technology more advanced than a light bulb or that scooter) is ever shown, suggesting that these happy couples have used Duet merely to plan the remarkable experiences they then put aside technology to enjoy. I couldn't help thinking that in real life, the lovebirds would have been tweeting pictures of their dinners or that sunset.

Even though it's Valentine's Day, before you succumb to the pressure to download a couples app, remember the warning of a character in D.H. Lawrence's Sons and Lovers: As he told his eager, would-be paramour, "You love me so much, you want to put me in your pocket. And I should die there smothered."

Rosen is a fellow at the New America Foundation and senior editor of the New Atlantis: A Journal of Technology & Society.