Discounting of course, the short-lived Tortellis spin-off. Is it true that after his show became a hit, Kelsey Grammer had it written into his contract that no other spin offs of Cheers could air while his show was on?

Well there was poll on which character should have their own spinoff and Norm had a high percentage votes.

They were all interesting characters and could have had spin offs, if the writing was good.