iMessages app is missing after update of OSX to Mountain Lion I have updated my Mac Mini to Mountain Lion.

I had iMessages beta installed on OSX Lion but after upgrading it's disappeared and now I don't have any iMessages.

I checked various sources for it with no luck. I also tried to reinstall the beta, but wasn't able to do that, either.
The chat tool which supports iMessage in Mountain Lion is called Messages.  Try searching for "Messages" in Spotlight, and loading the application.