Via Twitter, MuscleNerd announced the release of the Chronic Dev Team's iOS4 jailbreaking tool, greenpois0n. This follows some controversy in the jailbreaking community, after George "geohot" Hotz released his limera1in jailbreak tool one day before greenpois0n was due to be released, using a different hole in Apple's security.
Chronic Team members chose to halt the release of their own tool and change it to use the security hole Hotz discovered. This way, they still have the "SHAtter" exploit they previously discovered and initially based greenpois0n on. There's a chance that when Apple closes Hotz's exploit, SHAtter will still work.
At present, the tool is Windows-only; the "Mac" download button on the page doesn't go anywhere. The team promises a release "soon" for OS X and Linux. Currently, it supports iPhone 3GS/4, iPod Touch 3G and 4G, and the iPad. Apple TV 2G and iPod Touch 2G support will come in a later release.