Mystery Solved! What That Odd Kitchen Gadget From the Thrift Store Actually Is

 Best Vegetables to Slice
Vegetable
Best For
Onions
Salads, soups, caramelizing, burgers
Cucumbers
Pickles, sandwiches, salads
Potatoes
Hash browns, scalloped potatoes, chips
Zucchini/Summer Squash
Gratin, stir-fries, baking
Carrots
Slaws, snacks, stews (peeled first)
Apples
Pies, crisps, lunchboxes (core first!)