Might be a volunteer seed from some hybrid squash that’s reverted to its components. In that case, neither the plant nor the fruit will be exactly recognizable, and the fruit will look and taste like exactly what it is, a random cross between several members of the squash family. And it probably won’t taste very good.
We get volunteer “squashkins all the time, and they turn out quite tasty. Most end up as winter types, but we also get some really good summer squash types out of them.
They’re free crosses between pie pumpkins, zucchinni, pattypan, acorn, kubocha, butternut, and cocozelle. They may even have a bit of the neighbor’s hubbard in them by now.