This is the Fiascone, or Re Umberto #tomato. It's native from the Amalfi coast, and is probably the father of more famous tomatoes like the San Marzano. First accounts of it is at the end of the 19th century, when was donated to King Umberto.
Was thought lost, until a few years ago some plants have been found, and now is a must have for every seed-saver in my area!
Strong plant, easy to cultivate, quite pest resistant, solid in drought. This specific ripe fruit is quite small because it was grown in pot, but the green on the side is the same variety grown in ground.