It’s a roguelike game, a variant of Oangband, which in turn is a variant of Angband.
FAangband is based on Oangband 0.7.0 (started by Leon Marrick, now maintained and developed by Bahman Rabii). Changes have been made principally with the intent of immersing the player in the world of Tolkien's Silmarillion late in the First Age. While it is certainly not perfectly consistent (all the bad guys are still alive; all the good guys are dead, or at least have lost their best equipment), an attempt has been made to remove as many anachronisms as possible.
