The Kitaev honeycomb model is one of the archetypal examples of topological phases of matter. It has played a crucial role in shaping our current understanding of quantum spin liquid phases in two spatial dimensions. In this talk, we will discuss the rich physics arising for generalizations of the Kitaev model to three-dimensional lattice structures. In these models the low-energy degrees of freedom are Majorana fermions that may form various (semi-)metallic states. I will give a comprehensive classification of the resulting quantum spin liquid phases, as well as discuss their properties and possible experimental signatures.