Sil-Q is, like many roguelikes, a fork of an earlier game. In this case it is forked from Sil, which itself was forked from Angband. Sil-Q tries to adhere closely to the same design principles and ethos as Sil.
The Angband of Sil-Q is the Angband of year 465 of Tolkien's First Age. In Tolkien's "Lay of Leithian" Beren and Luthien descend at that time into Angband to face Morgoth and to steal from him a Silmaril.
The player character starts just below the surface, having entered Angband, and must descend through 20 levels to face Morgoth in his throne room. Near the surface lurk Morgoth's lesser servants such as orcs and wolves, but as the player descends they will meet Easterlings, wights, balrogs and dragons among other foes.
There are no classes or levels, but instead as the player gains experience they distribute their competences between eight different skills. Improving in a skill allows the player to invest also in abilities related to that skill, and in doing so build themselves a unique character.