Back in June of 2011, Mitch ­Kapor was enjoying dinner on the outdoor patio of Legal Sea Foods in Harvard Square. At a nearby table, a pair of fresh-faced ­recent MIT grads were trying to impress a prospective investor, and Kapor, the founder of Lotus Development Corp., one of the first software giants of the PC era, couldn’t resist sending out a tweet: “Overhearing 2 entrepreneurs pitching low-end 3D printer to a VC.”

The entrepreneurs had never met Kapor, and they didn’t meet him that evening. But after a friend pointed out his tweet to them, they arranged for a get-together the next time Kapor was in town. Kapor, who now invests in start-ups like the transportation app Uber and the virtual world Second Life, warned that he didn’t invest in companies working on physical products. But he was dazzled by the prototype 3-D printer that David Cranor and Maxim Lobovsky had built, which in a few hours could transform three-dimensional objects designed on a computer — perhaps a new car body or Bluetooth earpiece — into actual models, made of a hardened polymer material.