  Electric weak links, the term used for those parts of an electrical circuit
that provide most of the resistance against the flow of an electrical current,
are important elements of many nanodevices. Quantum dots, nanowires and
nano-constrictions that bridge two bulk conductors (or superconductors) are
examples of such weak links. Here we consider nanostructures where the
electronic spin-orbit interaction is strong in the weak link but is unimportant
in the bulk conductors, and explore theoretically the role of the spin-orbit
active weak link (which we call a "Rashba spin splitter") as a source of new
spin-based functionality in both normal and superconducting devices. Some
recently predicted phenomena, including mechanically-controlled spin- and
charge currents as well as the effect of spin polarization of superconducting
Cooper pairs, are reviewed.
