  We consider the homology theory of \'etale groupoids introduced by Crainic
and Moerdijk, with particular interest to groupoids arising from topological
dynamical systems. We prove a K\"unneth formula for products of groupoids and a
Poincar\'e-duality type result for groupoids which are principal with orbits
homeomorphic to a Euclidean space. We conclude with a few example computations
for systems associated to nilpotent groups such as self-similar actions, and we
generalize previous homological calculations by Burke and Putnam for systems
which are analogues of solenoids arising from algebraic numbers. For the latter
systems, we prove the HK conjecture, even when the resulting groupoid is not
ample.
