  We introduce dynamical analogues of the free orthogonal and free unitary
quantum groups, which are no longer Hopf algebras but Hopf algebroids or
quantum groupoids. These objects are constructed on the purely algebraic level
and on the level of universal C*-algebras. As an example, we recover the
dynamical SU_q(2) studied by Koelink and Rosengren, and construct a refinement
that includes several interesting limit cases.
