VideoLAN ---- VLC media player
VLC is a portable multimedia player, encoder, and streamer supporting many audio and video codecs and file formats as well as DVDs, VCDs, and various streaming protocols. It is able to stream over networks and to transcode multimedia files and save them into various formats.
About VideoLAN

VideoLAN is a software project, which produces free and open source software for video, released under the GNU General Public License.
About VLC media player
VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols. It can also be used as a server to stream in unicast or multicast in IPv4 or IPv6 on a high-bandwidth network. It doesn't need any external codec or program to work.
How to install:
VLC for Mac OS X is distributed as a disk image. Download the .dmg file, open it, and copy VLC to your hard drive (for instance the /Applications folder). Open VLC by double-clicking on it.
Download VLC Media Player for MAC
Download Windows Media Player