After releasing redsn0w 0.9.7b1, b2, b3 now redsn0w 0.9.7b4 for untethered iOS 4.2.1 jailbreak is out there under tester program of iPhone Dev Team.
According to official blog:
“The fourth beta is now available (testers ONLY please!). Starting with this version, redsn0w no longer requires you to install and run a separate program for the usbmux (this was a non-trivial procedure for many). It’s okay to keep that program running if you normally use it for ssh anyway. We also think we’ve fixed a race condition in the GUI that was causing redsn0w to crash during the “Preparing JB Monte Files” step. Nothing at all has changed on the iPhone side (where the main issues are still just Bluetooth and Skype).”
Right now, these beta versions of redsn0w are only for Mac users whereas Windows users will also get these in further update.
Download Redsn0w 0.9.7b4 for iOS 4.2.1