This is the untethered exploit installed by the TaiG 8.1-8.3 jailbreak tool. If you jailbroke your device with TaiG 8.1-8.3, this untether has already been automatically installed for you.

Version 2.1.3 of this package removes some now-unneccessary TaiG's uicache files, and speeds up boot time on the iPhone 4S.

Version 2.1.2 of this package makes Cydia Substrate work correctly (no update to Substrate is required: just install this).