Nice haul!
Don't take this as gospel (always have to be a little cautious with mystery fruit), but just going by what I can make out in the pic they look an awful lot like Valiant. To have a little better idea would ask for a pic of the vine but guessing the leaves are pretty much done by now.
If they are Valiant, they make awesome juice and jelly and you should be able to substitute Concord grape recipes (similar taste). Only asterisk being you have to deal with all of the seeds that are in them. If you run into a need for cheese cloth, dollar stores sell it on the cheap.
When I've worked with mine it's been in early September. Maybe someone with more experience in harvesting later in the season can give you a better idea, though did pick a bonus one off the vine the other day and it didn't taste half bad!