Simmer it uncovered over low heat until it reduces
Stir in tomato paste
Add a cornstarch slurry and cook briefly
Mix in a small amount of flour paste and simmer
Add mashed cooked vegetables or fruit
Stir in a little honey, molasses, or brown sugar
Use xanthan gum sparingly
Blend in more barbecue rub or dry seasoning
Add a small amount of instant mashed potato flakes
Let it cool, then refrigerate to thicken further