Redsn0w is a program that is used to jailbreak an iPhone or iPod touch. The jailbreaking process is what allows you to run custom application on your iPhone or iPod.
[Updated for iOS 5.1.1 & iOS 6 - Redsn0w 0.9.15b3 ]
The iPhone Dev Team has just released another update for Redsn0w 0.9.7 to fix Skype issues on iOS device. Redsn0w 0.9.7b6 is available for Mac OS X users only and in next version, the target will be adding iOS 4.1 monte so you don’t need to pirate iOS 4.2b3 to allow untethered jailbreak on iOS 4.2.1.
The iPhone Dev Team has released yet another update to Redsn0w 0.9.7 jailbreak tool. This new version fixes all sandbox-related issues, including Bluetooth problems on an untethered iOS 4.2.1 jailbreak. Also added is an “anti-piracy plea” note as a warning for those of you who are pirating iOS 4.2 beta 3 firmware.