Tune Buster Home Edition

Tune Buster Home Edition is a full-featured keyboard synthesizer for OS X, and will turn your musical keyboard into a complete instrument.

Tune Buster is easy to use and no configuration is needed, just start the program, plug in a keyboard and play.
Different sounds can be selected by clicking the desired instrument in the popup menu. Use the arrow keys or the mouse scroll button if you have one to speed up the selection process.
Tune Buster Home Edition can be made invisible by closing the main window, and the keyboard will still play. Choose