DH's name is Kristoffer, pronounced KrisTOFFer instead of the normal KRIStoffer. (I wouldn't recommend changing the pronunciation of such a common name--very confusing.) I've always called him Kristoff, but most of his family and everyone he works with calls him Kris.
I knew someone once named Cristian (pronounced Kriss-tee-AHN, accent on the last syllable), and his wife called him Tatan. I don't know if that was their own thing, or a common nickname in the Spanish-speaking country where he came from.
We call our Christopher CJ sometimes (and always when typing or writing, LOL). His middle name is Jacob. I really like Kit, gonna have to start using that one We use Chris a lot. And sometimes Topher, but always joking-didn't know people actually used it as a name! For me, Topher always flashes a mental image of a gopher. :LOL
I went to school w/ a kid who went by "Pher", as in fur. His sister was Jessica, but went by Jec. I think both names evolved from the kids mispronounciations as little kids, and just stuck. Jec writes for the local paper now, and still uses jec