Jailbreaks versions 3.1, 3.1.1 and 3.1.2 of Apple's operating system for iDevices.
The website link will provide you with a Mac or Windows version of blackra1n.
blackra1n is a program that jailbreaks versions 3.1, 3.1.1 and 3.1.2 of Apple's operating system for iDevices, known as iOS.
The program allows users to install the Cydia, Icy (removed in blackra1n RC3), and Rock package managers. These applications allow the user to access tweaks, homebrew applications, the root directory and the file system of the iDevice. Blackra1n can also perform tethered jailbreaks on the iPod Touch 3G and the iPhone 3GS, if the devices are running OS 3.1.2. When iOS 3.1.3 was released, SpiritJB had come out, and was untethered for both 3.1.2 and 3.1.3.