  In the framework of the PDE's algebraic topology, previously introduced by A.
Pr\'astaro, {\em exotic $n$-d'Alembert PDE's} are considered. These are
$n$-d'Alembert PDE's, $(d'A)_n$, admitting Cauchy manifolds $N\subset (d'A)_n$
identifiable with exotic spheres, or such that $\partial N$, can be exotic
spheres. For such equations local and global existence theorems and stability
theorems are obtained.
