significant software

 Download from the project page on CodePlex. 

Replayer is a free media player for use during rehearsals with playback music. It’s main feature is fast navigation to predefined cue points in the playback media.
Visual functioning of Replayer
First, you create a compilation of tracks and cues once. Then, using Replayer and your laptop computer, you can rehearse any portion of your set with ease. For fast navigation, use the numeric keypad.

For more information, see the Leaflet, the and the project page on CodePlex.

See also quirli, which is Replayer as a web app.