2mm Kolibri
The 2mm Kolibri (also known as the 2.7mm Kolibri Car Pistol or 2.7×9mm Kolibri) was the smallest commercially available centerfire cartridge, patented in 1910 and introduced in 1914 by Franz Pfannl, an Austrian watchmaker, with financial support from Georg Grabner. It was designed to accompany the Kolibri semi-auto pistol or single-shot pistol, both marketed as self-defense weapons, but somewhat underpowered.