This is the starfruit, sometimes known as the carambola. They're native to Indonesia and the Indian sub-continent, but they're grown widely in Taiwan. Wild varieties, smaller than the fist-sized ones you'll see in markets, are also fairly common. Often eaten fresh, starfruit can also be turned into juice. Personally I dislike the taste, but that doesn't mean you shouldn't try one.
In Chinese they're known as yáng táo (楊桃). Taiwan exports this fruit to Russia and other markets.
This photo is courtesy of Craig Ferguson.