Who invented those musical instruments?

You will see most of the greatest ones comes from Italy.

Violin

The answer is we probably know who really did make the first true violin. His name was Andrea Amati, and he lived in the northern Italian city of Cremona in the 15th century. The first violin we have made by Andrea Amati even has a date - 1465! It's thought that A. Amati's first violins were made about 10 to 30 years before that.

Piano

The piano is thought to have been invented in 1709 in Italy by Bartolomeo Christofori (1655 - 1732). He called his new instrument 'Gravicembalo col piano e forte' or harpsichord with soft and loud.

Guitar

The earliest extant six string guitar was built in 1779 by Gaetano Vinaccia (1759 - after 1831) in Naples, Italy. The Vinaccia family of luthiers is known for developing the mandolin. This guitar has been examined and does not show tell-tale signs of modifications from a double-course guitar.

Cello

The earliest known cello was made in Italy. At first called Viola da gamba, it literally meant "leg viola" as no endpin was used at that time and the cello was held resting on the player's calves; contrast "Viola da braccio", "arm viola". Through its development the Viola da gamba was a fretted instrument that could have 5 or 6 strings. Other non fretted varieties did exist but were generally considered to be of the basso variety and not a predecessor of the cello.

Saxophone

Saxophone was invented by Adolphe Sax, in 1840. He was a born in Belgium and was known as an instrument-maker, flautist, and clarinetist working in Paris. For 15 years, he did not receive his patent for this instrument. He manufactured these saxophones in almost all sizes and finally received his license on June 28, 1846. During the patent time i.e, 1846-1866 only the Sax company could manufacture saxaphones.