(From wikipedia)
The Aleph
In Borges' story, the Aleph is a point in space that contains all other points. Anyone who gazes into it can see everything in the universe from every angle simultaneously, without distortion, overlapping or confusion. The story continues the theme of infinity found in several of Borges' other works, such as The Book of Sand
Tlön, Uqbar, Orbis Tertius
In the story, an encyclopedia article about a mysterious country called Uqbar is the first indication of a massive conspiracy of intellectuals to imagine (and thereby create) a world known as Tlön
The Garden of Forking Paths
According to Noah Wardrip-Fruin and Nick Montfort, "The concept Borges described in 'The Garden of Forking Paths'—in several layers of the story, but most directly in the combination book and maze of Ts'ui Pên—is that of a novel that can be read in multiple ways, a hypertext novel.
The Book Of Sand
The titular "Book of Sand" is the Book of all Books, and is a monster. The story tells how this book came into the possession of a fictional version of Borges himself, and of how he ultimately disposed of it.