If you, or someone you know, makes a lot of cakes, this Layer Cake Slicing Kit would be pretty useful. It’s a metal collar, of sorts, that guides your knife through the cake, making for a perfect cut every time. From the site:
All you do is secure the slicing mold around the cake and slice along the evenly spaced grooves for up to eight even layers. Then use your cake lifter to place a cut layer on your cake stand, top with some homemade filling or buttercream, and then repeat until complete.
While this may qualify as a unitasker, it looks like it makes cake baking a lot easier. $60.