Frederik Pohl wrote a series of novels in which an alien species who attained faster than light space travel left for parts unknown and were thoughtful enough to leave behind a bunch of operable space boats where the descendants of Australopithecus could find them if they were able to get out of Earth's gravity well. The second title in the series is called Beyond the Blue Event Horizon.

These beings, called Heechee in the books, left a bunch of small objects in the boats which humans couldn't figure out what to do with. They called them "Heechee prayer fans" and kept them as souvenirs. Turns out that's not what they were. (No spoilers).