This is a services that lets you categorize your contact and then harness that organization when sending online invites. Handy!

Brilliant description of not providing cross-platform support.

...and from Microsoft!

"Unfortunately, we're not cool enough to run on your OS yet. We really wish we had a version of Photosynth that worked cross platform, but for now it only runs on Windows.

Trust us, as soon as we have a Mac version ready, it will be up and available on our site."