William A. Gilbert has released JarBundler 1.8 (forked from Seth J. Morabito's JarBundler 1.4) an Ant task for creating Mac OS X application bundles.
This version adds several minor features including the ability to specify
MIME types for the document. and a bundle attribute
fopr identifying documents which
are in reality directory trees, but are treated as a single entity by the Finder.
If you're using Ant to build Mac applications, you need this task.
JarBundler is published under the GPL.