Some authors who have written classics are Shakespeare, Chaucer, Cervantes, Niccolo Machiavelli, [Lao Tzu]?, and Confucius.
Classics in this sense make up what some call a canon of world literature. The question of what belongs in the canon of Western literature and art is a matter of much dispute (see Western canon).
Most "classics" are at least 100 years old, but sometimes we press the word into use to praise newly-created works.
Most classic books are in the public domain due to their age, and are freely available online from Project Gutenberg at http://promo.net/pg