Dripwn is an open source tool created by Munnerz to extract the Zephyr firmware files from Apple restore IPSWs. Version 1.x only works with OS X, while version 2.0 can extract the Zephyr files from any device connected to a Mac. There is also a command line utility that can be used with Win32/Unix systems.
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A free program for Mac, by Pocket Bits LLC.
