  Motivated by the recent interest in cosmologies arising from energy density
modifications to the Friedmann equation, we analyse the scaling behaviour for a
broad class of these cosmologies comprised of scalar fields and background
barotropic fluid sources. In particular, we determine the corresponding scalar
field potentials which lead to attractor scaling solutions in a wide class of
braneworld and dark energy scenarios. We show how a number of recent proposals
for modifying the Friedmann equation can be thought of as being dual to one
another, and determine the conditions under which such dualities arise.
