Also Strugatsky's "Roadside Picnic" - the "picnic" in question was a visit of aliens on Earth for unknown reasons. They came, they went, no one has actually seen them but they left their trash on our planet, "artifacts" in zones that are cordoned off by governments of Earth - from infinite batteries to multiplying gels and various gravity fields that will rip you apart in a second.. Like you said, some people ascribe all kinds of intentions to this visit, but most likely it's an encounter with a bug for them - they just left their stuff without as much as noticing us at all.

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pavel_lishin 7 days ago | parent [-]

Even the "trash" hypothesis is just that - one of the theories of why this stuff was left behind!

	▲	gambiting 7 days ago \| parent [-]
		Well yes, that's the beauty of it - the protagonist just makes a living hauling this stuff out of the zone(this is where Stalkers came from!), but in the novel there are various factions that believe all kinds of things - that these items are a gift from god, that they are trash, or that they are a test of some kind for us as a human race. I really do highly rate the book, it's great.