Apple has released their replacement app for iChat named Messages in Beta through their website.
Apple Messages would come preloaded with the next Mac OS X edition named Mountain Lion.
Send unlimited iMessages to any Mac, iPad, iPhone, or iPod touch.*
Start an iMessage conversation on your Mac and continue it on your iPad, iPhone, or iPod touch.
Send photos, videos, attachments, contacts, locations, and more.
Launch a FaceTime video call and bring the conversation face-to-face.
Messages supports iMessage, AIM, Yahoo!, Google Talk, and Jabber accounts.