It seems that no one's taken the time to mention the repeating crossbow and the polybolos for the sake of being technical about the crossbow family. :I
Well, alright, I suppose the polybolos is just far too large for any sane, normally-built man to manhandle solo, but this is just a reply for the statement that crossbows are slower than bows:
Chinese repeating crossbow: http://www.youtube.com/watch?v=Uo13R_fSvnI
Battery-powered auto-crossbow: http://www.youtube.com/watch?v=QS4RKoRyTik
Auto-xbow variant: http://www.youtube.com/watch?v=BSjCY2kGyfI
This one has to be my absolute favorite: http://www.youtube.com/watch?v=RCBA2oNzoiU
The same favorite crossbow, explained: http://www.youtube.com/watch?v=iAgSO5kty5w