Recently, we introduced the concept of plate mechanical metamaterials—cellular plates with carefully controlled periodic geometry and unique mechanical properties—as well as its initial realization in the form of freestanding corrugated plates made out of an ultrathin film. We used atomic layer deposition (ALD) and microfabrication techniques to make robust plates out of a single continuous ALD layer with cm-scale lateral dimensions and thicknesses between 25 and 100 nm, creating the thinnest freestanding plates that can be picked up by hand. We also fabricated and characterized nanocardboard – plate metamaterials made from multiple layers of nanoscale thickness, whose geometry and properties are reminiscent of honeycomb sandwich plates or corrugated paper cardboard. Ultralow weight, mechanical robustness, thermal insulation, as well as chemical and thermal stability of alumina make plate metamaterials attractive for numerous applications, including structural elements in flying microrobots and interstellar light sails, high-temperature thermal insulation in energy converters, photophoretic levitation, as well as ultrathin sensors and resonators. I will briefly discuss our experimental progress on all these applications, including demonstrations of extremely robust thermal insulators that can sustain a temperature difference of ~1000 K across a micron-scale gap, hollow AFM cantilevers that offer greatly enhanced sensitivity and data acquisition rates, and macroscopic plates that levitate when illuminated by light.