In the 80's Kac studied the number of representations of a quiver over a finite field k showing for example that their number is given by a polynomial in the size of k. In this talk I would discuss the analogous problem with k replaced by a finite ring, for example the integers modulo a power of a prime. I will discuss results (joint with T. Hausel and E. Letellier) as well as several conjectures on this topic.