RedSnow 0.9.7 beta 1 is available for download for Mac OS X.
RedSnow 0.9.7 implements the backup plan to iOS 4.2.1 untethered jailbreak.

This first beta release only supports:
*iPad
*iPhone4
*iPod Touch 4G

This is just a beta release. So, it can be erroneous. As per development team of iPhone, one should not even test this release. It’s not for general public. Also, don’t rely on ultrasn0w carrier unlock.

Known Bugs listed by development team of iPhone
*Bluetooth is disabled.
*You will face Springboard crash if using Task switcher. However, you can use Sbsettings process list as a temporary fix.
*iPod Player is only working with ipt4g.

Currently, dev team has released the version only for MacOS X. Soon, Windows version would also be released.
Download RedSn0w 0.9.7 Beta1 for MacOS X for untethered iOS 4.2.1 here

To untether, select “Jailbreak Monte“