I just made braised beef short ribs with a red wine & beef stock reduction, and I have about 4 cups of the sauce left over. What can I make with it?

For budget stuff:
How about in Swedish meatballs over pasta, or a Salisbury steak with peppers, onions and mushrooms. Or shank steak (cooked in a pressure cooker with the sauce and a bit more wine. All super thrifty meals.

Turn it into a fabulous beef stew.

How about turning it into a savory pasta sauce? You might cook short curly pasta until not quite done, mix it with the leftover sauce, top with breadcrumbs and grated cheese, and pop it in a hot oven for 15 minutes or so. Call it pasta al forno con avanzi (meaning baked pasta with leftovers, but the Italian sounds a lot sexier).

I have exact same issue from dinner last night- I'm going to use some as gravy for a meatloaf planned later in the week and freeze the rest to use as a starter for French onion soup, or to add to a meaty tomato sauce, or to bolster a mushroom barley or lentil soup. Way back when I would make several briskets a week, I would save up the gravy and them turn it into a kick ass Sweet & Sour Cabbage soup- which is like if beef vegetable soup and stuffed cabbage had a beautiful soupy baby. I think of it as Super Stock.

Freeze in smallish portions (half cup or cup) to use for future dishes when you want them. Thin with water to make beef risotto. Add some onions, croutons & gruyere cheese for a version of French onion soup. Add some cooked rice or noodles for a simple soup.

I'd add sauteed mushrooms , okra , butternut squash and sliced jerusalem artichokes; cover and simmer til okra and squash are done; serve over pasta or grain- couscous would be excellent. You could even make that sauce moroccan flavored by adding some chile flakes,cumin, allspice, a little cinnamon... (google moroccan stews)