Dave Cotter was an executive at Internet giant Amazon when his marriage collapsed. His divorce spawned the kind of logistics challenges that sophisticated algorithms couldn’t solve: how to coordinate with his ex on the care of his three daughters, and how to remain part of their special moments, even when he couldn’t be there.

After he left Amazon in 2011, Cotter decided to pursue his own solution to these problems. His Seattle-based startup, SquareHub, has raised nearly $1 million from such Seattle-based angel investors as AOL board member Dawn Lepore and Amazon senior vice presidents Jeff Wilke and Brian Valentine. The service, which launched in May, is small but growing. It allows the “tens of thousands” of families that Cotter says have signed up so far to establish private groups and share calendars, photos, and status updates from their phones without exposing any private information to advertisers or the general public. “We are trying to build a digital family room, a place where everyone is essentially in the same place, sharing the kind of information that used to be on the fridge,” Cotter says.

Ray Wang, an analyst with Constellation Research, says private messaging services are increasingly popular antidotes to wide-open social networks such as Facebook and Twitter. “Not everyone wants to be out there and to keep trading privacy for convenience,” Wang says. SquareHub is “tapping into this family demographic that has the basic problem of scheduling and tracking events. They’re creating a nice place where users trust privacy.”

SquareHub functions as a kind of mashup of other social networks, including Facebook, Twitter, Foursquare, and Evite, but with high walls to keep out the public. Parents install the app on their kids’ phones or tablets and they can share photos and updates, make plans, and assign events to shared calendars.

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