Foobar2000 is an audio player for Windows. Some of its features include a low memory footprint, ReplayGain support, and built-in support for several popular audio formats.
It is also extendable with plugins, and has an open API for plugin development. Unlike players such as Nullsoft's Winamp, or Lycos' Sonique, Foobar2000 does not natively make use of skins, following the edict of "It's just music. We just play it. Quit Slacking." that I find myself in favor of.
Its interface has been referred to by many as "Similar to Windows Notepad", or spartan, with its utter simplicity. There is a textual list of songs displayed in its window, with a menu bar on top. One may double-click on a title to play, or use the control buttons offered to play, skip, fast-forward or otherwise.
One of its more interesting features is Tabbed Playlists. Taking a page from the concept of tabbed browsing, Foobar2000 allows users to create a number of 'tabs' that may hold individual playlists, which many see as a bonus.
The player also has a much more flexible tagging system which allows for checking things, such as empty fields in a given file's tag, and a choice to display or not display this. This is excellent for people who have music with incomplete tagging, but want a nearly uniform look
This player was created by Peter Pawlowski, who has also done work on plugins for Winamp, version 2, as an alternative to the steadily growing bloatware and ads that Nullsoft's parent company, AOL, seems to forcibly inject with each new iteration.
Foobar2000 currently runs on Windows 95/98/ME, Windows 2000/XP, and has been reported to run on Linux under WINE.