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Founded in 2011, Windsor’s software helps online retailers boost business from repeat customers by analyzing purchase history and behavior and then using that information to automate customer loyalty and product recommendation programs. Some of its customers have included L’Oreal, Ghirardelli Chocolate and Lenovo.

Windsor has been one of the most successful companies to come out of the downtown tech incubator American Underground in recent time. In 2016, it moved its offices into the top floor of the historic Trust building at 212 W. Main St. in downtown.

The company has raised more than $14 million in venture capital since it was founded, including around $1.1 million last year. In 2016, Windsor Circle was named to the Inc. 5000, the ranking of the nation’s fastest-growing private companies. Windsor Circle grabbed the No. 351 spot on the list.

Williamson called the sale a good outcome for the company’s investors and noted that several parties had been interested in buying Windsor. Some of Windsor Circle’s investors include Durham-based IDEA Fund Partners and Triangle Angel Partners.

“Can't comment on investor returns as that is confidential,” he said, “but suffice it to say that our board was deeply involved in the process, supportive in both patience and advice, and that this is a solid outcome.”

Lister Delgado, a managing partner at IDEA Fund, said he was glad to see Windsor Circle be acquired.

“We are glad to see another one of our portfolio companies arrive at an exit,” he said. “Matt Williamson and his team have worked very hard over the years to build Windsor Circle. We are proud to have been there since the very beginning and helped in some small way take the company to this point.”

Windsor has seen its ups and downs, however. The decision to sell the company comes almost a year after the company laid off around half of its staff – going from 65 employees to 35.

Windsor said at the time that it was no longer targeting small and mid-size companies for its services, which eliminated the use of some jobs.

Williamson declined to say how many people Windsor currently employs.

Founded in 1992, Windsor’s new owner, OSG, builds technology for billing and invoice services. It has acquired several online marketing startups in the past few years – and, last year, the company itself was bought by the private-equity firm Aquiline Capital Partners.

OSG CEO Scott W. Bernstein said in a press release that Windsor’s technology would immediately be used to bolster another startup it recently bought, WhatCounts, an email marketing company.