Karaboss is primarily a MIDI sequencer, but it has gained additional features over time and is now capable of handling musical XML files (which it converts to MIDI), playing MP3 files—a common feature, to be sure— but also MP3s containing synchronized lyrics (less common), CDG files (an ancient, prehistoric format), and finally KFN files.
Karaboss is a free MIDI Karaoke player, Sing karaoke like a boss!