How does Waiting for Godot relate to Sartre's Huis Clos (No Exit), in which it is concluded that hell is other people?
The title of Sartre's play in French is literally translated "Closed Door." The three main characters in the play are literally behind a closed door that allows no exit.
In Waiting for Godot Vladimir and Estragon are waiting for the never appearing Godot.
These plays fall into the category of theatre of the absurd, or absurdist drama. Absurdism is defined as "an avant-garde style in which structure, plot, and characterization are disregarded or garbled in order to stress the lack of logic in nature and man’s isolation in a universe which has no meaning or value." Isolation is heavily stressed in both plays.
Additionally, both Beckett and Sartre espoused existentialist philosophy, which "rejects the idea that the universe offers any clues about how humanity should live." Sartre simplified it by saying, “Existence precedes essence.” That is, the fact that we exist is all that matters, and we don't need to find some higher meaning to life.
Some scholars have said that "Godot" really is God; thus the playwright is telling us that God is not going to come. Just as Sartre's characters are trapped in a room that has no exit, so also Beckett's characters are trapped in a meaningless existence, constantly waiting.