Kam* helicopters

Interesting trivia:

Kamov is a Russian aircraft manufacturer that sells helicopters with coaxial contra-rotating main rotors. That means two sets of rotor blades: one on top, one on the bottom. They rotate in opposite directions.

Kaman is an American aircraft manufacturer that sells helicopters with intermeshing contra-rotating main rotors. That means two sets of rotor blades: one on the left, one on the right. They rotate in opposite directions (think about it—it works like an egg-beater).

Contra-rotating rotors in either coaxial or intermeshing format are really rare, so it's remarkable that the only two large-scale manufacturers of helicopters in this arrangement are otherwise obscure, have nearly identical names, and are situated on opposite sides of the atlantic.