SquareDeskPlayer is an open-source cross-platform (Mac, Windows & Linux) tool for Modern Western Square Dance callers. It includes a music player, a lyrics editor, and a powerful graphical checker mover (SD).

Definitive information at http://squaredesk.net/

A built-in lyrics editor provides a super-simple way to edit cuesheets.
These cuesheets can be automatically scrolled during singing call playback, to make it easy to learn or perform a song.

For singing calls, the transport bar clearly shows you where you are in your opener, break, closer, and each sequence

Track how long it's been since you've played a given song for any day of the week! Helps you rotate your music so dancers don't get sick of it.

Quickly design new sequences with a built-in copy of SD, with a clean graphical front-end, supporting automatic group/station annotation.