The dynamic that unfolds is somewhat reminiscent of “Her,” the 2013 Spike Jonze film in which Joaquin Phoenix’s character falls in love with an operating system. With Karen, however, it’s not the user but the app that starts exhibiting inappropriate behavior. “She develops a kind of friend crush,” Mr. Adams said. “And over the next 10 days or so, she feeds back to you things she’s learning about you — including some things you’re not quite sure how she knows or why.”

One other thing that’s different about Karen: It’s not a movie. It’s a personalized experience that plays out on a smartphone or tablet. There is no fourth wall. There is no Joaquin Phoenix. This story is about you. It morphs to fit the user, based on information the user supplies, choices the user makes and inferences the app itself begins to make. And just as you reveal yourself to Karen, she reveals herself to you, in ways that veer farther and farther from a legitimate life-coach experience.

Beginning April 16, shortly after it’s scheduled to be available for free download on Apple’s app store, Karen will be featured in the Tribeca Film Festival’s Storyscapes competition, which showcases innovative, interactive approaches to storytelling. “I love the idea of a life coach that goes wrong,” said Ingrid Kopp, director of interactive at the Tribeca Film Institute and curator of the competition. “And I thought it would particularly appeal to New Yorkers.”