map-all.clj

(defn map-all
  "Sequence of results from applying f to the first of each of colls.
  Empty colls are dropped and evaluation proceeds."
  [f & colls]
  (lazy-seq
   (when-let [s (seq colls)]
     (cons (apply f (map first colls))
	   (apply map-all f (for [coll (map rest s)
				  :when (seq coll)]
			      coll))))))

user> (map-all vector [1 2 3] [4 5] [6])
([1 4 6] [2 5] [3])