This fruit is unmistakable because it has five (sometimes more) prominent ridges down its side. Green when unripe and sour to set your teeth on edge (lovely with a dash of salt) but sweet-sour and yellow when ripe.
I saw the top part of this tree covering the roof of a small stall on the road I take to work. The tree was behind the stall so I did not get to see it in entirety. I am just surprised that the local urchins have not looted the fruits...or the owners (if any) have not harvested it for sale.