FORTUNE -- Joe Lonsdale is what an earlier generation would have called a young man in a hurry. A protégé of investor Peter Thiel, Lonsdale helped him build Clarium Capital into a multibillion-dollar hedge fund. Then, again with Thiel, Lonsdale co-founded Palantir Technologies, a security analytics software firm.
Having made a small fortune in his twenties -- he recently treated himself to a 30th birthday party at Hearst Castle on California's Central Coast -- Lonsdale has set his sights on a new challenge: designing software for the ultrawealthy. Addepar, his three-year-old startup, aims to apply Silicon Valley smarts to the increasing complexities faced by the super-rich in tracking, analyzing, transferring, and reporting their finances. (The name is Latin wordplay based on a line in Ovid's Metamorphoses meaning "Add a little to a little and you'll have a great amount.")
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Addepar charges several hundred thousand dollars per year for its software, depending on the size of a customer's assets. It connects family offices or endowments with the various entities that manage their money, facilitating fund transfers, generating speedy reports, tracking currency conversions, and cutting down on data-entry errors. With the first handful of clients representing more than $100 billion in assets, Addepar says it generates annual revenue of about $12 million. (It doesn't charge a fee for all assets.) It is close to breaking even, thanks in part to a lean staff of 75 in relatively inexpensive offices in Mountain View, Calif. "We'll be able to grow two to three times a year for at least five years," says Lonsdale.
To complement coders, Lonsdale has recruited a sales force that is tight with its clientele. Company president Mike Paulus hails from a prominent timber and agriculture family in the Pacific Northwest. Top client-relations executives include Justin Rockefeller, son of the West Virginia senator, and Aidan Crawley, a nephew of the Duke of Westminster. Harrison LeFrak, of the New York real estate family, praises Addepar's ease of use: "It doesn't require a Ph.D. to read the instruction manual."
Lonsdale says Addepar's platform will eventually benefit any institution that manages money, including pension funds and mutual funds. "It's not about making rich people richer," he says. "It's about making the global finance system better."
This story is from the September 24, 2012 issue of Fortune.
Update: An earlier version of this story misstated the annualized revenues of Addepar. It generates $12 million, not $25 million. The firm also no longer charges customers a fixed fee of 0.05% of assets managed. Addepar says customers pay "several hundred thousand dollars a year," depending on their assets.
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