The Fantasia in F minor by Franz Schubert, D.940, for piano four-hands, is one of Schubert's most important works for more than one pianist and one of his most important piano works altogether. He composed it in 1828, the last year of his life, and dedicated it to his pupil Caroline Esterházy.
The above text from the Wikipedia article "Fantasia in F minor for piano four-hands" text is available under CC BY-SA 3.0.