Along with the announcement on the next version of OS X, Apple decided to give a us a “sniff” of the new Lion with a beta release of Messages. It’s not just the iMessage app on the desktop and laptop machines.
You can use it with an iTunes account, like iMessage, but also with AIM, Yahoo!, Google Talk and Jabber accounts. You can use it to send text, as well as photos, videos, contacts, locations and even other attachments. It will be deeply integrated with FaceTime.
If you can’t seem to get a download going from the official page, try this one.