What it is: Apple's instant-messaging client gets its usual overhaul to accompany a major OS X update. In the past, that's meant features such as video and audio conferencing, compatibility with other chat protocols and Bonjour support.
This time around, Apple's added a number of features, which we outlined when Steve Jobs first previewed the Leopard version of iChat last August.
Under Leopard, iChat adds tabbed browsing, a new "invisible" status to hide your online presence from your many admirers, the ability to record audio and video conferences, Photo Booth-like video effects, and the ability to show slideshows, movies or presentations during iChat conferences - Apple dubs this last feature iChat Theater.
What's changed: That August 2006 preview of iChat included a Screen Sharing feature, in which you can control the Mac of another conference participant. That feature appears to be incorporated in the Finder in the latest iteration of OS X 10.5.
Judging by Steve Jobs' WWDC keynote, Apple has added a number of new effects to iChat - or at least shown effects that it didn't show off last August. These include a Princess Leia-style hologram and the ability to overlay your lips over someone else's portrait.
iChat Theater continues to allow you to show off presentations and files during a chat session - the new detail is that any file type compatible with Leopard's Quick Look feature will work in iChat Theater.
Another, more practical addition to iChat is the use of the AAC-LD ("LD" for "Low Delay") audio codec. Apple says this widebrand codec samples a full range of vocal frequencies for better-sounding audio chats. DAN MOREN AND PHILIP MICHAELS