Given the news that has already come out about Facebook, you’re probably thinking there is no way that anything else leaks out today. They’re probably on lockdown (real lockdown, not the crazed coding “lockdown”), right? Wrong.

We’ve learned about the existence of yet another secret project within Facebook . And while it’s not quite as sexy as the new Photos app, the ramifications of it are much larger. Say hello to Project Spartan.

As we understand it, Project Spartan is the codename for a new platform Facebook is on verge of launching. It’s entirely HTML5-based and the aim is to reach some 100 million users in a key place: mobile. More specifically, the initial target is both surprising and awesome: mobile Safari.

Yes, Facebook is about to launch a mobile platform aimed squarely at working on the iPhone (and iPad). But it won’t be distributed through the App Store as a native application, it will be entirely HTML5-based and work in Safari. Why? Because it’s the one area of the device that Facebook will be able to control (or mostly control).

Facebook will never admit this, but those familiar with the project believe the intention is very clear: to use Apple’s own devices against them to break the stranglehold they have on mobile app distribution. With nearly 700 million users, Facebook is certainly in the position to challenge the almighty App Store distribution mechanism. But they need to be able to do so on Apple’s devices which make up a key chunk of the market.

As of right now, there are believed to be 80 or so outside developers working with Facebook on Project Spartan. These teams are working on apps for the platform that range from games to news-reading apps. Some of the names should be familiar: Zynga and Huffington Post (owned by our parent AOL), for example. The goal is to have these apps ready to roll in the next few weeks for a formal unveiling shortly thereafter.

Work has been going on for at least a couple of months, with Facebook putting in a lot of work before that. So some of the apps may not be fully polished at launch. It may be more of a “look what we can do” type thing.

Reached for comment on the matter, Facebook said they had “nothing to share”. But we don’t need their confirmation. Why? Because I’ve seen Project Spartan with my own eyes.

Imagine loading up the mobile web version of Facebook and finding a drop-down for a new type of app. Clicking on one of the apps loads it (from whatever server it’s on depending on the app-maker), and immediately a Facebook wrapper is brought in to surround the app. This wrapper will give the app some basic Facebook functionality, as well as the ability to use key Facebook elements — like Credits.

One thing the App Store has nailed is an easy payment system. Facebook has been attempting to build the same thing with Credits, but so far hasn’t done much in the mobile space. With Project Spartan, they intend to have Credits built-in to allow developers to sell apps and offer in-app purchases. This will be vital for a partner like Zynga, for example.

Speaking of Zynga, it has been known for some time that Facebook was placing a huge emphasis on making it easier for game developers to build with HTML5 as opposed to Flash (like Zynga and others currently do). The culmination of this will be Project Spartan.

And while the target may ultimately be Apple, in this regard, they’re somewhat helping Apple by killing off yet another huge piece of Flash reliance on the web: gaming.

But again, the real goal is to get people using Facebook as the distribution model for games and other apps, not the App Store (or any other distribution hub).

Much has been made recently about Apple’s partnership with Twitter over iOS 5. It’s widely believe that Facebook was once the preferred partner, but was snubbed — or did the snubbing, for one reason or another. Regardless, the implications are clear: Twitter will be the big single sign-on partner for iOS, not Facebook, even though that’s a key area of focus for them. So they’re taking the fight to the browser.

Android will also clearly be a part of this new platform. But we’re told that the initial target is definitely mobile Safari on iOS devices.

Things are about to get a lot more interesting in the mobile space. More to come.