Gulliver's Travels and Robinson Crusoe are alike in being fictionalized travel adventures that draw their inspiration from popular travel narratives in their period. Both are first-person narratives describing the protagonist's adventures in other parts of the world. Gulliver's Travels, however, is a satiric fantasy while Robinson Crusoe is an early realist novel.
The creatures that Gulliver encounters in his travels are fanciful: they do not exist in real life. They emerge so that Swift can satirize or poke fun at the weaknesses and failings of Europeans, especially the British. For example, Swift mocks the pretension of English politics and the English court through his depiction of the unusually tiny Lilliputians, who are not as threatening as they believe:
I perceived it to be a human creature not six inches high, with a bow and arrow in his hands, and a quiver at his back.
These tiny people are vindictive, violent, and self-deluded, which is how Swift saw the British government. For example, when they want to kill the innocent Gulliver for treason, the king's counselors' tell him that there is
a sufficient argument to condemn you to death, without the formal proofs required by the strict letter of the law.
Nobody, outside of perhaps a child, thinks the Lilliputians are real, any more than one does a fairy or elf.
Defoe, on the other hand, tries to make Crusoe's adventures on a deserted island as realistic as possible. He introduces nothing that could not occur in real life. Crusoe's island is completely devoid of any fantastical creatures like Lilliputians or talking horses. Crusoe, too, is utterly pragmatic in making us of real elements on the island:
I found an excellent use for these grapes; and that was, to cure or dry them in the sun, and keep them as dried grapes or raisins are kept
Robinson Crusoe is also a colonialist narrative in a way Gulliver's Travels is not. Gulliver visits various places for a period of time, but always as an observer. Even in Lilliput, which he could have conquered, he has no interest in dominion. In contrast, Crusoe exerts control and ownership over his environment, asserting his right to take the land as his own. He is delighted when he can
think that this was all my own; that I was king and lord of all this country indefensibly, and had a right of possession; and if I could convey it, I might have it in inheritance as completely as any lord of a manor in England.
If Crusoe acts on his environment, Gulliver is acted on: he is gullible, as his name implies, and easily impressed by what he sees.