Actually if you're talking about the Chinese crossbows, they're actually called repeating crossbows. The Chinese variant is called the Cho-Ko-Nu (or something like that, there's a few different spellings). Wikipedia page: http://en.wikipedia.org/wiki/Repeating_crossbow
Frankly it seems that the Cho-ko-nu wasn't that great of a weapon by itself per se, since it didn't have as much power as a normal crossbow. However, used en masse, it was dangerous as hell, especially if the arrows were poisoned. Which was why it was still in use up until around 1900 in Chinese armies.
Anyhow, there have also been Graeco-Roman equivalents, although these were larger and were more like anti-personel or small artillery weapons rather than the smaller Chinese ones, and according to a couple of TV shows I can't name right now, it is possible to engineer a crossbow (using the technology of back when) with near machine-gun speed using a crank.
EDIT: In my conworld, this is why I have crossbows become a main weapon of most civilizations when they reach the equivalent of our late medieval or early renaissance technology (along with a bit of clockpunk). These crossbows basically become like machine guns, which is why a World War I-esque style of combat develops and reaches its peak during a 200-year conflict between the largest empires of this time, Aidis and Cedarin (and then throw in other stuff like Chinese-style rockets, Greek Fire flamethrowers, late medieval grenades and mines along the styles of China, a little bit of clockpunk machinery, and good old-fashioned swordfighting, and you got a huge mess on the battlefield).
I have a blog, unfortunately: http://imperialsenate.wordpress.com/
I think I think, therefore I think I am.