aliens crashing and their ships being a dungeon has been part of dnd since 1st edition
The Mindflayers are pmuch aliens who travelled back in time so they win, the neigoi(sp) interdimensional(intergalactic) slavers, at least one insectoid hive mind thing of aliens that are basically Alien/zerg/nids, there's a group of humanoids from the far realms that have unnatural living ships and crash in the material plane, etc.
Expedition to Barrier Peaks and Temple of The Frog are the old core modules with space stuff.
“The entity sighting reports were even more perplexing. It seemed that the aliens were forever picking up plants and rocks. When they chanced to speak to an observer, they often asked bizarre questions like “What is your time frame?” or made odd statements, as when a farmer investigating an uproar in the yard one night found strange entities trying to corner one of his terrified hunting dogs. “We come in peace,” he reported them saying. “We only want to take your dog.” As the years passed and abduction reports became more numerous, the same pattern of odd behavior associated with UFOs was reinforced: alien repetition of certain activities beyond what seemed logical to ufologists, and, given the years of exposure the presumed extraterrestrials had had with Earth, surprising naivete about human behavior. This lacuna in alien knowledge became apparent as increasing numbers of abduction reports surfaced and baffled many—investigators and abductees alike. One abductee trying to prevent another alien encounter reported that he went to bed clutching a crucifix. When he woke up one night with the familiar paralysis and sense of alien presence, he began praying. As the aliens approached his bed, one of them noticed this behavior and asked what he was doing, to which the other responded, “Oh, he’s just practicing his religion,” and they took him anyway. Yet another abductee reported that he had tried to prevent an abduction by winding string all around himself before he went to bed at night. This person reported that as the aliens approached his bed they stopped, stared at the string, and, not knowing what to do with a trussed victim, turned around and left without him.”
There's an ancient RTS game called Dark Colony. It's not /tg/ at all, but a fun thing about it is that most game files are plain text, so you could modify it with great ease for some hilarious results.
In Within the ring of fire the Grey(that is legit their name, as well) exist as a "playable" species. They are intelligent shapeshifters brought to the fourth world(standard setting) by the elder creator of Darkness, Ahriman whom delighted in their assistance in destroying the third world for it. Their faith Ahriman in the face of global cataclysm convinced the elder creator that they as a species were worth of continuing, and then put them in timeless oblivion until they are needed again. Now with the rise of the fourth world Ahriman has placed them into reality to yet again lead this world into an apocalyptic end.
They are intelligent shapeshifters(they gain a new humanoid apperance they can use each level, with 10 being maximum.) whom are sadistic and cruel by nature. they live to infiltrate the societies of the world and strive to drive them into extinction, ever faithful in Ahriman and it´s plan for perfection.
The probings are important to our culture, stop hating you racists.