From the iPhone Dev Team’s Wiki:

What is it?

A cross-platform jailbreaking, unlocking, and customizing tool for iPhones and iPod touches. Customizations include boot logos, recovery logos, and “verbose” boot. It’s a standalone program that doesn’t use iTunes (no custom IPSWs are involved).

The download links are at the bottom of this page (but please read the whole page anyway!).

We’ve been offering redsn0w in various incarnations over the years (including poorlad’s Windows version of QuickPwn). The most recent release before this one was redsn0w 0.8, which targeted Apple firmware 3.0/3.0.1.

» More information and download here…