And while we're talking about obscure fruits with Z's in their names...

I recently came across this fairly thorough discussion of Syzygium species from the Philippines on the blog Market Manila, with the common names "makopa" and "tambis". The discussion features a number of photos and spans three posts:

Tambis / Makopa / Curacao or Malay Apple
The Tambis (Syzygium Aqueum) Chronicles, Take II…
Tambis & Makopa Side By Side…

I don't really know much about the Myrtaceae. I was reminded of these posts because Syzygium sounded kind of like Ziziphus, and had it in my head that the two fruits looked kind of alike (although not so much, now that I look at them again). I thought maybe they were related, but no, not remotely--they're not even in the same order.