George Hotz, whom you may remember as the teenage hacker who originally unlocked the iPhone, has let loose a jailbreaking app for the iPhone 3GS code-named “Purplera1n”. It enables the installation of third-party software not approved for Apple’s App Store.

Presently, purplera1n is Windows-only (this does not include Windows 7) and requires the latest iTunes version be installed, as well as an iPhone 3GS with the 3.0 firmware.

In a blog post titled “I make it ra1n,” Hotz says a Mac version is “Coming shortly.”

Hotz notes that he normally doesn’t make tools for the general public and would rather wait for the iPhone dev team to do that.

"But guys, what’s up with waiting until 3.1? That isn’t how the game is played," he says on his blog. "We release, Apple fixes, we find new holes. It isn’t worth waiting because you might have the ‘last’ hole in the iPhone. What last hole…this isn’t golf. I’ll find a new one next week.

John Biggs over at CrunchGear is among those who have already given purplera1n a go and declares the jailbreaking process "amazingly simple."

But take note: Hotz does caution that purplera1n is in beta and suggests backing up your data before running the app.