Winamp is a free, skinnable multi-format music / media player made by Nullsoft that can currently be used on either Windows or MacOS operating systems. It gained popularity in the late 1990s especially with the proliferation of the MP3 music format.
Winamp2 is currently on version 2.91 (as of August 2003). Winamp3 is a more recent version that is more user friendly and offers more features, but many users found it too resource-hungry and switched back to Winamp2. Nullsoft also seem to have stopped developing Winamp3 and recently unofficially released a beta version of Winamp 2.92.
Winamp3 can play MIDI, MOD, MP1, MP2, MP3, vorbis, WAV, WMA, OGG and many other formats. It also supports a wide variety of plugins allowing more input and output formats; and sound and visual effects. Such plugins are available both at the official website and from other parties. Some of the plug-ins enable Winamp to play console emulator related sound formats which are NSF, GBS, SID, HES, GYM, SPC, PSF, and PSF2.
A number of similar programs exist based loosely on the same user interface design and program capabilities but made by independent parties, often running on other operating systems. Two such programs are MacAMP and XMMS.