Jailbreak community is doing an amazing job, the day Apple releases the updated version of iOS, and the developers release the Jailbreak tool. Like Apple released iOS 6 beta 3 earlier this day, soon after that, iPhone Dev team updated the redsn0w to add support for iOS 6 beta 3. Just like iOS 6 beta versions this is also for the developers only.
This version of redsn0w supports only A4 devices [iPod Touch 4G, iPhone 4 and iPhone 3Gs] and after Jailbreaking your iDevice, Cydia will not be installed on your iDevice but you will be able to SSH into your iPhone so this is a developer only version. Moreover, this is a tethered Jailbreak which means if your restart your iDevice, you will need to connect it with PC. Last but not least, if your iPhone relies on unlock then you should stay away from iOS 6beta 3 as well as Jailbreak.All in all, Jailbreak process is similar to that of previous version of Redsn0w, but before Jailbreak point to iOS beta 3 and then run the Jailbreak. Here’s what the Dev team posted on their blog:

The “dev3” version covers today’s 6.0beta3 release (and also adds explicit support for 6.0beta2). Please point redsn0w at the 6.0b3 IPSW in order to jailbreak beta3 and boot tethered.

Download Links:Redsn0w 0.9.13dev3 (OS X)Redsn0w 0.9.13dev3 (Windows — run in Administrator Mode)