  We define $\Delta$-equivalence for operator systems and show that it is
identical to stable isomorphism. We define $\Delta$-contexts and bihomomorphism
contexts and show that two operator systems are $\Delta$-equivalent if and only
if they can be placed in a $\Delta$-context, equivalently, in a bihomomorphism
context. We show that nuclearity for a variety of tensor products is an
invariant for $\Delta$-equivalence and that function systems are
$\Delta$-equivalent precisely when they are order isomorphic. We prove that
$\Delta$-equivalent operator systems have equivalent categories of
representations. As an application, we characterise $\Delta$-equivalence of
graph operator systems in combinatorial terms. We examine a notion of Morita
embedding for operator systems, showing that mutually $\Delta$-embeddable
operator systems have orthogonally complemented $\Delta$-equivalent corners.
