The founders of Entrustet are surprisingly young. Jesse Davis , who is 23, was still a student at the University of Wisconsin when he wrote the original business plan in 2008. He came up with the idea after reading what has become one of the best-known stories on the complexities of digital assets and one of the few that has found its way into the courts. Justin Ellsworth, a Marine killed in Iraq in 2004, did not leave behind the password to his Yahoo e-mail account, and when the company refused to give his parents access to it, they sued. Eventually, under orders from a probate judge, Yahoo gave them a CD it said contained Ellsworth’s e-mail. Ellsworth’s story convinced Davis and his business partner, Nathan Lustig, 25, that there was a market for “digital estate planning” services. In the case of Entrustet, this means an automated system for storing passwords and instructions for all your digital assets.

Such businesses rest on a simple idea: Web, mobile and social-media use keeps exploding; everyone still dies. Meanwhile, much of the archiving of basic family life is becoming digital. It has become routine to have an online “presence” even as an infant, by way of a picture posted on a parent’s social-networking profile. Lustig pointed me to a recent corporate study that identified “chief memory officer” as a kind of unofficial role taken on by someone (often mom) in many families — the person who is paying attention to the idea that there may be no physical scrapbook or set of journals to hand down to future generations and that bits-and-bytes memory objects need to be preserved somehow. Trendwatching.com has predicted a “burgeoning market” for products and services that protect the digital content that is “the nucleus of one’s personal brand.”

I spoke to a couple of Entrustet users, who said they particularly wanted to protect photos stored online, along with hosting and domain-­registration information for personal and business sites. Entrustet also offers an “account incinerator,” to obliterate content its users would prefer not to have linger on after them, and one person I spoke to mentioned having tagged a personal Twitter account for deletion — “it’s just inside jokes, personal ranting and raving” — along with a Gmail account. “I don’t need people judging the personal e-mails that I sent to my friends,” he explained.

Given the degree to which the most popular online platforms involve promoting a quasi-public persona — the “you” who declares fandom of Bob Dylan and Flannery O’Connor, but not the “you” who binges on “Jersey Shore” reruns and TMZ.com — this instinct seems logical. If we try to control the way we are perceived in life, why not in death, too? It’s not wholly unusual to do this with physical artifacts: letters to be opened only after death, or even to be destroyed. If you don’t want your heirs figuring out that you had a secret Tumblog clogged with pictures of Natalie Portman, maybe you should just arrange for it to be “incinerated.” If nothing else, those Entrustet users figure they are leaving behind some guidelines about which bits of their online lives matter, and which don’t.

Most people do not leave such directives, making the fate of their digital lives uncertain. One of the better-known instances of a disappeared digital legacy involves Leslie Harpold, a Web pioneer who died unexpectedly in 2006, at age 40. Her writing and other online projects connected her with friends and admirers who were helping create the Internet’s self-expression tool kit back in the mid-1990s. In early 2010, after her sites Harpold.com and Smug.com quietly disappeared, some of those friends lobbied Harpold’s family to let them preserve her work. “Her work is her legacy,” one admirer, Rogers Cadenhead, wrote to Harpold’s niece, Melissa Krauskopf, an attorney who served as the personal representative of Harpold’s estate. “I have corresponded with several of Leslie’s friends about her sites all disappearing from the Web. For what it is worth, all of us believe that she would not have wanted that to happen.”

This offer was declined. Harpold’s niece replied that Harpold’s legacy isn’t in her online work but rather “is with every person who knew her and loved her.” I spoke to Krauskopf briefly, and while she was cordial, she had little to add. Had her aunt left directives about her online work, they would of course have been honored, she said. But in their absence, the domains were part of the estate that went to Harpold’s mother, and while Krauskopf appreciates the perspective of her aunt’s Web friends, it was a family decision that doesn’t require public explanation. “People need to appreciate that she was a real person,” Krauskopf says, and the family prefers to “remember her as she was.”

You might think that stories like that would inspire at least the most cutting-edge true believers in the importance of online expression to stampede digital-afterlife-management companies. But Entrustet and its rivals acknowledge facing a variety of challenges, from an estate-planning community that isn’t particularly tech-forward to convincing potential customers that the start-up meant to deal with their digital afterlife will still be a going enterprise by the time they die. I tried out Entrustet myself. It seems to ease the unwieldy process of sorting out what to do with lots of online accounts with different passwords and so on, but I would add another challenge to the list: it’s depressing. I made my wife my “digital executor,” which meant that she received an e-mail about her responsibilities that she found jarring and a little chilling, even though I’d warned her. The idea of updating this thing every time I change a password or try out a new social Web tool that I may or may not keep using seemed even less enticing than cleaning out the attic.