A slab that delays one polarization by 1/2 wave with respect to the other is a half-wave plate. A circular one rotates polarization by 90 degrees; a linear one flips one diagonal to the other diagonal and exchanges left and right circularly polarized light.
A slab that delays one polarization by 1/4 wave is a quarter-wave plate. A circular one rotates by 45 degrees; a linear one converts diagonal light to circular light and circular light to the other diagonal.
Two pieces of dichroic material with different axis directions can be made into a Wollaston prism. This takes light of two different polarizations and sends them in different directions. With a quarter-wave plate switch, this is used as the detector in quantum cryptography.