Mercury Messenger

Mercury Messenger requires no personal information to sign up - after installation, you simply need to select a screen name.Afterwards, you can search for other screen names and immediately begin chatting by tapping on the screen name.
All messages in any chat can be edited an infinite amount of times or deleted permanently for both users, even if they have already been read.

The online, full functionality, version of this app can be found at:
http://hypermarkgo.com/MinimalChatApp/index.html