Webamp
webamp.org
A pixel-accurate web recreation of Winamp 2.9 that plays MP3s from your local files or URLs — including the equalizer, playlist editor, visualizations, and support for thousands of original Winamp skins.
Why it is useful
A remarkable piece of reverse engineering — every detail of the original Winamp interface is faithfully reproduced in pure JavaScript, including the visualization system and the skin file format. The skin gallery has thousands of user-created skins. Beyond nostalgia, it's an impressive demonstration of what modern browser APIs can do. Still functions as a perfectly usable music player for local files.