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iNdependence is a Cocoa-based application for Mac OS X which provides an easy-to-use interface for jailbreaking, hacktivation, SSH installation, and managing ringtones/wallpapers/applications on your iPhone. It's open source under the GNU v2 license.
The source code for interacting with the iPhone has been broken out into a library (libPhoneInteraction) so that it can be easily reused by other applications.