Icelandic folklore says that the horseshoe-shaped canyon of Asbyrgi in northern Iceland was made by the imprint of Sleipnir's hoof (source: Dictionary of Northern Mythology. p. 294).
The name Sleipnir means "slippy" or "the slipper" in Old Norse (source).
In kennings, metaphorical compound nouns common in Germanic poetry, Sleipnir's name appears as a word for ship: "sea-Sleipnir."
American lumberjacks also told a story about an eight-legged horse, which they nicknamed "Old Spider-Legs" (source: Mythical Creatures of the North Country).
When someone dies among the Gondi people of India, they sing a funeral dirge that refers to his funeral bier (which is carried by four people) as the horse with eight legs (source: Gods and Myths of Northern Europe. p. 142-143.).