ono
"Over aNd Out"

This is used to end a conversation usually in a instant messaging situation, possibly may be used in a non-real-time communication method such as E-Mail.

This normally is the last thing one says after "bye", "cya", "pce out", etc. It's a way to stop un-ending exchaning of "Bye"(s) at the end.
Person 1: ok then, i'll see ya on monday !
Person 2: sure, and don't forget the home-work !
Person 1: yea ok bye now
Person 1: ono
Person 2: ok bye cya
Person 2: HEY what page is the homework again ?!
Person 2: HELLO ?!? You there ?!
Person 2: :S