I agree--it's a mixer lift. Here's a link that shows how it works:

Pull it out straight towards you until the entire flat surface is completely out of the cabinet. Then, when you pull a little further, you will feel the platform start to lift and then swing backwards towards the countertop. Be careful to keep your hands on the front of the platform as those springs are very strong and snap back toward the cabinet with a vengeance. You do not want to get your hand caught!

If you can't get the lift to pull straight, you may need to apply WD40 or similar and work the mechanism a couple times before attempting to raise it to its upper position.

We have one of those platforms in an old desk where it was used to hide the original manual typewriter...it makes a handy spot for a computer printer although we only pull it forward, not raise it to the upper position

Thank you all! After living here for 4 years, I am finally using the mixer lift! Actually my food processor fits perfectly and is now off my counter - yippee! Who knew? Does anyone know where I can get more of the metal things that hold the adjustable shelves in place in the other cabinets

Home Depot or lowes should have the shelf holders

go to sears, Home depot, Lowes or Menards and look in the specialty hardware part.