An XVID file is a video file encoded with the Xvid codec. Xvid is an open source codec that uses MPEG-4 compression. While XVID files are not natively supported by most popular video players, they can be played once the Xvid codec is installed.
Microsoft Windows Media Player with Xvid codec
Media Player Classic with Xvid codec
Eltima Elmedia Player
Apple QuickTime Player with DivX and Xvid codec
Xvid for SuSE Linux
Xvid for Debian