I can't do better than to quote The Daley News, an Australian tree nursery, on this fruit:
Fruit Tree of the Month
Santol - Sandoricum koetjape
Native to Asia the Santol is a large fast growing and attractive tree. In their native setting they can grow to around 45 m with a large buttressed trunk and branches low to the ground.
In cultivation they are more commonly seen as a 15 m specimen tree. In Asia the santol is valued not only for its fruits but it is also grown as a timber and shade tree, although the timber is not of high quality it does polish well.
The fruits are large, round and rough on the outside with a thick textured yellowish skin. The flesh is segmented around the 3-5 seeds, they are called lolly fruits as the flesh sticks firmly to the seeds and it is best removed and enjoyed by sucking the seeds clean. Do not be tempted to swallow the seeds.
I find these fruit (or at least the 'lolly' part) to be as insipid as so many other South East Asian fruit, a sort of jellified sweet flesh with a flavour so goddam subtle that I have difficulty describing it. And the flesh sticks to the seeds like slimy cotton wool. However,the orange skin is marvellous; very tart, and solid.
I've used it to make some very, very acceptable chutney, the kind that nearly substitutes for Branston Pickle, the essential ingredient for a genuine cheese-and-pickle sandwich.