I’m pretty sure it’s a video format, but I have this .OGM file and I have no idea what to use to play it. Something freeware/shareware would be preferable.
windows media player will but will need some extra bits. See http://ld-anime.faireal.net/guide/ogm-en for info
Its a Ogg Media wrapper Any media player can play it with the appropriate codecs.
Check out Zoom Player:
And yes, you also need the extra bits in scm1001’s link.