We’ve been extensively covering the roll out of the latest version of Redsn0w, using which you can easily untether your iOS 4.2.1 jailbreak. We reported earlier this month that the latest version of Redsn0w would be released around Christmas, and indeed it was, the beta 1 of Redsn0w 0.9.7 was released on the given date, along with warnings related to this test program. However, to fix the issue of native app crashes that arose in beta 1, the iPhone Dev-Team then launched beta 2 of Redsn0w 0.9.7 and then for specifically fixing bugs related to non-GUI programs, beta 3 of Redsn0w 0.9.7 was released. Now, the iPhone Dev-Team has launched beta 4 of the latest version of Redsn0w, more details about it given below.

Primarily, one of the major improvements in beta 4 will be that Redsn0w 0.9.7 will no longer require you to install and run a separate program for the usbmuxd, and also, the iPhone Dev-Team believes that beta 4 just might be the last big code change to Redsn0w 0.9.7, and if this goes well, a Windows version may be released soon. Reminder: Redsn0w 0.9.7 is currently a Mac-only test program.
The iPhone Dev-Team says:
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).
Please note that if you’ve been testing the previous betas, and your device is already jailbroken on any particular one of them, perform a fresh restore before testing Redsn0w 0.9.7b4.
Download Redsn0w 0.9.7b4 from here.