updated 09:15 am EDT, Mon October 11, 2010
Windows-only for time being
A new jailbreaking tool has been released for iOS devices, dubbed Limera1n. The software is capable of jailbreaking most devices running iOS 4.0 or later, including the iPad, the iPhone 3GS and iPhone 4, and the third- and fourth-generation iPod touch. The Apple TV is also "technically supported," though there no apps available for it, whether officially sanctioned or otherwise.
The jailbreak is still in beta, and while allowing handhelds to operate untethered, still has some important limitations. It is first of all Windows-only; a Mac version is said to be "coming soon." Installation also isn't a one-click process, though this is described as a necessary tradeoff. Instructions are included with the download.