Microsoft SharedView now available without an invite

SharedView (previously codenamed "Tahiti") is now available without an invite. SharedView will let you connect up to 15 friends or co-workers to your computer so they can see your screen. Sessions can be initiated through Windows Live Messenger and up to 200MB worth of files can be shared with the connected viewers.

According to the FAQ, audio and chat are not yet available, but if you're using Windows Live Messenger anyway, you can always go that route.