There is only one file type that uses the .KFN extension:
KaraFun Karaoke File
File created by KaraFun, a program for editing and playing back karaoke music; saved in a proprietary format and contains MIDI audio as well as lyrics text and display animation settings; used for playing karaoke songs.
KFN files can be exported to various multimedia formats using the KaraFun Editor, which is included with the KaraFun installation.
Updated: August 19, 2011