All natural (mostly) wood stains! A handful of pennies in vinegar will produce a beautiful pale Caribbean blue stain. A wad of steel wool will give you a rich reddish hue. A combination of tea and a metal object in vinegar will produce a black stain.
Traditional paste wax is still the best way to renew and enhance natural wood finishes, and it will hold up better than liquid furniture polish. All you need for application is an old t-shirt and plenty of elbow grease. Clean, apply and then polish.
I would recommend doing it outside as it stinks and the rust from the steel wool will stain concrete so do it in a shop or over the road. DIY Vintage Wood Stain look. (How to age new wood). Good for all things wood!