3 Gallons of Cider turned Vinegar - Suggestions on Use?

Not being a smart arse here but you can use it for weed/grass killer.

Clean mould from cellar, bathroom etc

If it's done turning into vinegar, filter out the impurities including the "mother", bring it to 180° to kill any remaining bacteria let cool and you will have great tasting vinegar.

Mark’s Not too Spicy BBQ Sauce

Simmer for 20 minutes and put into mason jars.
2 Cups Tomato Paste
2 ½ Cups Apple Cider Vinegar
½ Cup Sugar
¼ Cup Honey
¼ Cup Paprika
¼ Cup Black Pepper
1 TBsp Cayenne Pepper (or Ground up Red Pepper FLakes)
1 TBsp Salt

Mark’s Not too Sweet BBQ Sauce

Simmer for 20 minutes and put into mason jars.
2 Cups Tomato Paste
1 ½ Cups Chianti (Italian cooking wine)
1 Cup Apple Cider Vinegar
½ Cup Honey
¼ Cup Molasses
¼ Cup Sugar
¼ Cup Paprika
1 TBsp AllSpice
1 TBsp Granulated Onion
1 TBsp Kosher Salt
1 TBsp Ground White Pepper
1 tsp Whole Celery Seed
1 tsp Ground Ginger
1 tsp Granulated Garlic