VLC Player is pretty codec agnostic, it can play back almost all of 'em. You'd need an actual editing program. I'm not aware of any good free ones. If you just need to re-encode them to something ...

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. VLC ...