Developer website: iChatters.com
iChatters is a Dashboard widget that allows you to update your status on iChatters.com on the fly. Available for Cam Chats? Simply choose "Available" from the Dashboard Widget and you will get priority status listing on iChatters.com. Decide that you're not available? You can quickly set yourself to "Not Available" so others won't bother you.
Mac OS X 10.4 or later