foobar2000 (also known as FB2K according to setup) is a freeware, advanced audio player available for Windows OS. It offers full Unicode support, gapless playback, a customizable layout, advanced tagging capabilities (which makes it an excellent MP3 tagging tool), support for ripping audio CDs, support for all popular audio formats such as MP3, WMA, FLAC, MP4, WavPack, CD Audio, Vorbis, AAC and other rare formats. It is also famous for other things such as the low usage of your computer resources (CPU and RAM - which allows you to install it on slower PC's) an impressive customization process and features that are highly appreciated by audiophyles such as support for Asio, KernelStreaming, WASAPI which produces the "bit-perfect" output sound.
Important: When installing foobar2000 you are allowed to choose between the standard installation on your computer and portable. The portable mode does not support file association.