The VLC Media Player is an all-rounder. It plays just about any video & audio format there is, streams and converts media from one format to another. It is cross-platform, meaning it is available for not only different Windows versions, but for Linux, Mac & other platforms. Best of all, it is free.
This is how the official site describes it:
VLC is a free and open source cross-platform multimedia player and framework that plays most multimedia files as well as DVD, Audio CD, VCD and various streaming protocols.
