Mac OS X: Today Apple is releasing FaceTime for OS X (in beta), allowing OS X and and iOS users to quickly and easily video chat regardless of device.
You can start making FaceTime video chat calls to any iOS user (the iPhone 4 and fourth generation iPod touch) and other OS X users sometime today, as soon as Apple pushes their beta release. The download page isn't up yet, but we're guessing you'll be able to find it here (if Apple's normal URL structure holds up). There's very little to it beyond that. FaceTime video chats look like they work pretty seamlessly across between iOS and OS X.
FaceTime for Mac beta is a free download in beta, available for download later today.
FaceTime for OS X [Apple]