Looks like a young eggplant.

But I've never heard of an eggplant plant spontaneously popping up in someone's garden.

Joe

I can't really tell how large it is, but many nightshades make fruit that looks like that, many of them very poisonous.

May be a "Rose Hip"...possibly from a Rugosa or Multiflora Rose???

Rosie

Not a rose hip. Something Solanaceous. Can we see the plant and have some indication of scale?

The first 8 pictures in the batch I hope they are good enough to see

Here is a link that might be useful: flicker

Perhaps Solanum villosum

Here is a link that might be useful:

maybe a nightshade but i cant tell the size...