The jailbreak tool GreenPois0n is released by Chronic Dev Team which works to jailbreak iOS 4.1 devices including iPhone 4, iPhone 3GS, iPod touch 4G, iPod touch 3G and iPad.
Right now, GreenPois0n does not provide support to jailbreak iPod touch 2G and Apple TV which is expected soon.
Windows and Linux users could grab GreenPois0n from following download links whereas Mac users still have to wait for their concerned version.
You may also use Limera1n to jailbreak iOS 4.0 and iOS 4.1 which is available for Windows only.
Download GreenPois0n for Windows and Linux
Download iOS 4.1