The spinettone ("big spinet") was a kind of harpsichord invented in the late 17th century by Bartolomeo Cristofori, who was later the inventor of the piano.
[1] The spinettone was a kind of spinet, which means specifically that its strings were placed in pairs along a diagonal relative to the position of the keyboard.
[2] As Kottick (2003) points out, the design of the spinettone attested to the extraordinary ingenuity of its inventor, which has been remarked on by a number of modern scholars (see Bartolomeo Cristofori).
The spinettone that Cristofori built were intended for the Medici family of Florence, more specifically for his patron Prince Ferdinando, the son of Grand Duke Cosimo III and heir to the Tuscan throne.
Besides being smaller than a regular harpsichord, the spinettone had another advantage, pointed out by Kottick: owing to the diagonal geometry of the strings, the player could be seated more or less facing the performers on stage, while the sound was projected in the direction of the audience.