Vivaldi certainly belongs to the elite of classical European composers. And he was a busy fellow too [from Wikipedia]:

Over 500 concertos; approximately 350 of these are for solo instrument and strings, and of these about 230 are for violin; the others are for bassoon, cello, oboe, flute, viola d’amore, recorder, lute, and mandolin. Approximately 40 concertos are for two instruments and strings, and approximately 30 are for three or more instruments and strings. 46 operas, sinfonias and 73 sonatas.