Intuitive

Koopman-von-Neumann Mechanics is a reformulation of classical mechanics in the Schrödinger framework.

Usually in classical mechanics we use the Newtonian framework where our main focus are the trajectories of objects.

In contrast, in the Schrödinger framework our main focus are observables, states and measurements. This means, instead of describing the trajectories of objects, we now ask instead for example: If we measure the momentum of this ball, what's the probability that the result will be $10$ kg m/s?

Concrete

The equation of motion in Koopmann-von-Neumann mechanics is a complexified reformulation of the classical Liouville equation (which handles probability distributions over the phase space).

• See the notes by Frank Wilczek on "Koopman von Neumann Mechanics, and a Step Beyond"
• See also this nice answer at StackExchange

Abstract

Why is it interesting?

The Koopman-von-Neumann reformulation of classical mechanics is extremely helpful to understand the differences between classical and quantum mechanics. Usually these theories are describes in completely different languages which makes it hard to compare them. Using the Koopman-von-Neumann reformulation we describe classical mechanics in exactly the same language that we use in quantum mechanics and thus can perfectly analyze what is different.