VocalEasel is a simple MacOS X (10.5 or later) lead sheet editor and music rehearsal tool designed for the needs of Jazz vocalists, using LilyPond to produce printable lead sheets and MMA (Musical Midi Accompaniment) to produce MIDI accompaniments.
The latest versions of VocalEasel can be downloaded from the Download page. Be sure to download the binary version of the program, not the file ending with "_src", unless you're into programming.
You will also need to download a copy of LilyPond. VocalEasel will help you with that task when you run it without this app installed.
Use the menu items provided in the VocalEasel Help menu or go directly to the tracker page.