This isn't strictly a fermentable, but...
Anyone ever tried making pineau de Charentes, or pommeau?
Pineau is unfermented wine must blended with unaged brandy, then aged in wood and bottled around 20% ABV. Pommeau is the Norman equivalent that uses unfermented cider and apple brandy.
I made two bottles of the latter years ago by obtaining a good bottle of apple brandy (not calvados, though...the Lairds bonded stuff, full apple brandy, not the blended applejack) and mixing it 50/50 with Martinellis apple cider. Recapped, and it makes a nice sweet drink, like a liqueur.
Yesterday I did the same with a bottle of unfermented chablis juice, and a bottle of inexpensive American brandy, for a cheap approximation of pineau.
Very interesting I'd say! It would go well with certain foods I'm sure...cheese, certainly, with the sweet/acidic element.