[Update: This was a bust. There was no such device introduced on Monday.]

Score one for The Unofficial Apple Weblog (TUAW) — maybe.

Only hours before Monday’s opening of World Wide Developers Conference, they posted the first leaked photograph of a new Apple product — or what certainly seems to be a real product — and it’s not an iPhone.

It’s called Mac Fusion, according to the promotional copy that surrounds the photo, and looks like a mini-Mac Mini — or an Apple TV into which someone has cut a slot wide enough for a CD or DVD.

The headline in display type — “Bridge the gap” — fits the two-bridges theme set by Apple’s e-mail invitation. And it’s a product aimed at developers, which makes sense given that WWDC is, after all, a developers conference.

If this is a fake, it’s a very good one. The copy certainly reads like it came out of Apple’s (AAPL) marketing department:

“Building your applications for the Mac has never been easier. Mac Fusion was designed exclusively for new developers wishing to port their existing programs to the Mac without breaking the bank. Mac Fusion allows you to explore the power and stability of Max OS X while keeping the ability to run alternate operating systems such as WIndows or Linux, via Boot Camp.”

That’s not something intended for the consumer market. No price is indicated, nor shipping date, but there is a big Buy Now button on the page, which would suggest sooner rather than later.

[Photo courtesy of TUAW.]