What is this called it's from Taiwan?

It's called carambola, or starfruit.

http://en.wikipedia.org/wiki/Averrhoa_carambola

In Taiwan, it's called 楊桃 (young tao). It's very popular fruit in Taiwan.

http://zh.wikipedia.org/wiki/%E6%A5%8A%E6%A1%83

its a slice of mango fruit.

這是>楊桃..對於喉嚨非常有幫助.可以醃製.熬湯.果汁.等用途.

It is "starfruit". Among Taiwanese Mandarin speakers is it called "yang tao", and among Taiwan Hokkien speakers it is called "uign dou".