From the JUKEBOXMP3 web site:

Here at JUKEBOXMP3 we have developed a MP3 player that is NUMBER or mouse driven which means that you can type a NUMBER in the KEYBOARD and the SONG associated with that NUMBER will start to play. If another NUMBER is entered this song will be added to a play next list. We have also a PRINTLIST button and this will print out a list of all your MP3s with a number assigned to them.