VLC is a free and open source cross-platform multimedia player and framework that plays most multimedia files as well as DVDs, Audio CDs, VCDs, and various streaming protocols.

Plays everything: Files, Discs, Webcams, Devices and Streams.

Plays most codecs with no codec packs needed: MPEG-2, DivX, H.264, MKV, WebM, WMV, MP3

Can do media conversion and streaming.