Which opera by Alban Berg was left unfinished at his death?

Lulu is an opera in three acts by Alban Berg. Berg adapted the libretto from Frank Wedekind's two Lulu plays, Erdgeist and Die Büchse der Pandora. Berg died before completing the third and final act, and the opera was typically performed as a "torso" until Friedrich Cerha's 1979 orchestration of the act 3 sketches, which is now established as the standard version. Lulu is notable for using twelve-tone technique during a time that was particularly inhospitable to it. Theodor W. Adorno praised it as "one of those works that reveals the extent of its quality the longer and more deeply one immerses oneself in it."