We review the recent notion of a nonautonomous dynamical system (NDS), which has been introduced as an abstraction of both random dynamical systems and continuous skew product flows. Our focus is on fundamental analogies and discrepancies brought about by these two principal classes of NDS. We discuss base dynamics mainly through almost periodicity and almost automorphy, and we emphasize the importance of these concepts for NDS which are generated by differential and difference equations. Nonautonomous dynamics is presented by means of selected examples. We also mention several natural yet unresolved questions. KEY WORDS: nonautonomous dynamical systems; random dynamical systems; skew product flows; almost periodic equations; almost automorphic equations.