  Motivated by applications to geometric inequalities, Gozlan, Roberto, Samson,
and Tetali introduced a transport problem for `weak' cost functionals. Basic
results of optimal transport theory can be extended to this setup in remarkable
generality. In this article we collect several problems from different areas
that can be recast in the framework of weak transport theory, namely: the
Schr\"odinger problem, the Brenier-Strassen theorem, optimal mechanism design,
linear transfers and semimartingale transport. Our viewpoint yields a unified
approach and often allows to strengthen the original results.
