I thought about Cro's post 'using the valuable antique breadknife". I use a few things which haughtily believe that they should be standing cherished in a vitrine :-)
Here is my lovely Sheffield Grapefruit-cutter-set:
The case is made of brown reptile-skin (maybe not allowed to be sold today) - inside beautiful off-white silk and a funny little device in dark-blue velvet to keep the knife in place. The knife has a Faux Bone handle, the slim spoons are Silver Sheffield and of excellent use even if you don't cut the grapefruit before, because they have little 'teeth' on one side.
But I do cut the fruit - always.
I, then being very young, was so impressed when at breakfast they served us the cut grapefruit in Gosford Hall Inn - a beautiful listed hotel in Cumbria (now 350 years old), - we were there in 1976 - coming back from Scotland in our old blue Merc (1969 with tail fin). Coming home (to Mainz then), I cut a grapefruit every day myself.
I don't know when the grapefruit-cutter was made - maybe around 1940 or the beginning fifties?
Anyway: they are beautiful AND useful - thus I use them.