  We investigate arrangements of hyperplanes whose normal vectors are given by
connected subgraphs of a fixed graph. These include the resonance arrangement
and certain ideal subarrangements of Weyl arrangements. We characterize those
which are free, simplicial, factored, or supersolvable. In particular, such an
arrangement is free if and only if the graph is a cycle, a path, an almost
path, or a path with a triangle attached to it.
