The Decameron is a collection of stories by Giovanni Boccaccio, probably completed around 1353. It is set during the Black Death in Florence some years before, following a group of seven women and three men who flee the city for a deserted villa, passing the time by telling each other a series of tales over ten days.
This provides the occasion for a hundred stories, drawn from a variety of sources, in what would be one of the most influential uses of the frame-story device in Western literature.
Free online texts
Gutenberg: The Decameron, translated by John Payne. Multiple formats.
Internet Archive: The Decameron (Chatto & Windus edition, 1922). Multiple formats.
University of Adelaide (Internet Archive): The Decameron, translation attributed to John Florio (1620). Multiple formats.
Wikisource: The Decameron. Payne (1886) and Rigg (1903) translations. HTML and other formats.
Letterature Italiana: Decameron. PDF format.
Libero: Decameron - HTML format.
Wikisource: Decameron - HTML and other formats.
Brown University: Decameron Web - included texts and translations.
Librivox: The Decameron, translated by J.M.Rigg - public domain audiobook.
The Great Conversation: Further reading at Tom's Learning Notes
Paul the Deacon: History of the Lombards
Dante Alighieri: The Divine Comedy
Geoffrey Chaucer: The Canterbury Tales - A number of the tales imitate stories from the Decameron.
Marguerite de Navarre: The Heptameron
Christine De Pisan: Book of the City of Ladies
Shakespeare: All's Well That Ends Well
Jonathan Swift: A Tale of a Tub
Lessing: Nathan The Wise
Harold Bloom's Western Canon: The Decameron is listed.