The founder of the site, Natascha Drabbe, is an architectural historian whose personal interest in residential masterworks began after she acquired the home of the Dutch architect Mart Van Schijndel in the Netherlands. “We worked four years on this,” she said. “Every continent is represented.”

She found other modern-house museum curators who shared her interest in preservation and knowledge-swapping. They formed a committee to put together the list of properties that should be included. The group includes Lynda Waggoner, director of Fallingwater, the Frank Lloyd Wright house in Pennsylvania; Kimberli Meyer, director of the MAK Center at the Schindler House in Los Angeles; Iveta Cerna, director of Mies van der Rohe’s Villa Tugendhat in the Czech Republic; and Susanna Pettersson, director of the Alvar Aalto Foundation.

Ms. Drabbe said that making the houses more accessible to visitors would elevate interest in their preservation. “Now, if you’re visiting Paris, for example, our site allows you to see that you’re close to the only house Alvar Aalto built outside Finland. This information wasn’t so easy to come by before.”