Marelmo SNC is the company, and, I believe, the derailleur brand of Giorgio Marchigiano, Gianpetro Mogno and Luigi Ezzu of Torino, Italy. During the 1980s they developed a curious derailleur that used a large, effusively coiled, spring. In principle it was the bastard child of a 1950s pull chain, sliding rod derailleur. However, unlike most of its forebears, it was top-normal.

Unfortunately I don't believe that this wildly eccentric item ever made it into mass production.