It has definitely been an iPhone-friendly day on the interwebs. It was just a few hours ago that the iPhone 1.1.3 jailbreak was released to the public by Nate True (from cre.ations.net). However, this was a Windows-only version of the jailbreak; but Nate was working on a Mac version and has just released it!
You can download the Mac version of the software from the cre.ations.net website. Please note that this jailbreak might be hazardous to your iPhone's health. Before you jailbreak your iPhone, be sure to backup in iTunes -- and as always, hacking your iPhone is completely at your own risk.