Gianni Schicchi is an opera in one act by Giacomo Puccini to an Italian libretto by Giovacchino Forzano, based on a story that is referred to in Dante's The Divine Comedy. It is the third act of Il trittico. First performance: Metropolitan Opera, New York City, 1918.
Gianni Schicchi is only briefly referred to in Dante's Inferno. Canto XXX:
That grim vignette is not the real source of the opera's action. An anonymous Florentine commentary on the Commedia, first published in 1866, elucidating Dante's terse reference, is the actual source to the familiar plot set-up. 
Buoso Donati has died in bed. His relatives mourn melodramatically, until they hear the rumor that he has left all his money to the local monastery. They frantically search for the will. Rinuccio finds it, but refuses to release it to his aunt Zita until she agrees to his terms. If the will is favorable to him, she must allow him to marry Schicchi's daughter, Lauretta. After consenting, she reads the will, and he sends for Schicchi. When the will confirms the rumor, everyone is furious. They refuse to allow Rinuccio to marry. What can be done?! Schicchi and Lauretta arrive to a cold reception. Rinuccio insists that Schicchi can solve their problem, and they reluctantly agree to let him try. Schicchi sends his daughter away. After hearing that no one else knows of the death, he tells the arriving doctor that Donati is feeling better and that his services are no longer needed. Rinuccio runs for the notary. Schicchi will impersonate Donati and dictate a new will. The relatives agree to the division of the property, except for Donati's mule, mills, and house. They agree to let Schicchi decide who will inherit those items, but, one by one, they return to bribe him. Schicchi reminds all of the penalty for forgery. The notary arrives. While the relatives fume, Schicchi grants the mule, mills, and house to himself. After the notary leaves, he throws everyone out, and they are helpless to do anything. Now that Lauretta has a dowry, there is no obstacle to her marriage to Rinuccio. Schicchi asks for the audience's indulgence.