Like dfyx said, Jellyfin is a good free option, if you what another free(mostly) option, Plex is another good one which may be a bit more user friendly if all you want to do is stream your own media through the internet. If you want to only view files locally, then even a raspberry pi may suffice through some kind of local file viewer, but online (Plex, Jellyfin, etc) would be best for viewing on other devices too.