IcoFX
http://icofx.ro
http://portableapps.com/apps/graphics_pictures/icofx_portable

was used to create the windows .ico and mac .icns files.
It is free and easy to use.

Changelog:

v3 2010.10.25 (ede)
This is the revamped version of the plain kangaroo. The initials OJ are added to make better use of the square icon space and to increase the recognition.
The icon is based on the logo files from
http://jump-pilot.sourceforge.net/download/ojlogo/
.