  Only few selected examples among the great diversity of anomalous rare earth
skutterudite are reviewed. Focus is first given on PrFe4P12 in comparison with
URu2Si2. For PrFe4P12, great progress has been made on determining the nature
of the order parameter (OP). A non magnetic order parameter with a multipolar
component emerges here while for URu2Si2 the nature of the so-called hidden
order remains mysterious. The two systems have several similarities in their
temperature--pressure (T, P) and magnetic field--temperature (H, T) phase
diagrams, in their spin dynamics, in their nesting character and in their high
sensitivity to impurities. Advances on one side must stimulate new views on the
other. Besides general considerations on the choice of the OP, a simple basic
problem is the treatment of the Kondo coupling in a system with low charge
carrier number for the cases of uncompensated and compensated semi-metal. An
interesting problem is also the possible decoupling between exciton modes and
itinerant carriers.
