perspective control lenses allow either tilting of the lens away from the sensor plane or shifting the lens parallel with the sensor plane, or both
tilting is primarily used to create greater depth of field (DOF) by aligning the plane of focus with your subject's plane which is a common technique for traditional landscape photographers
tilting can also be used in the opposite way to reduce depth of field (DOF) and this effect is sometimes also used to create a “diorama” or “fake miniature” effect where the shallow DOF of life size scenes makes them appear to have been close up shots of model scenes
shift is mainly used to allow photos of tall buildings while keeping the camera itself parallel with the ground to minimise keystoning effect
shift can also be used to create 3 images which can later be stitched into a panorama
currently there are no high quality dedicated true tilt or shift lenses designed for Micro Four Thirds system, however, given the short lens flange to sensor distance, it is possible to use a number of other solutions
also of note, Olympus cameras now have keystone correction functionality which somewhat reduces the need for shift lenses
some manufacturers are producing lens mount adapters which incorporate tilt, shift or tilt-shift functionality which effectively converts a full frame non-tiltshift lens (especially Nikon lenses) into a tilt or shift lens
unfortunately, currently most (except the Lensbaby and Fotodiox) do not include aperture control so are best used with lenses with aperture rings
most non-tiltshift lenses are not optimised for this work so expect to see lots of CA and aberrations on extreme tilt or shift
tilt shift adapters are complex designs and some may have too much play and lack build quality, but they do make a far cheaper option than buying a dedicated tilt shift lens, although in the end you may prefer to bite the bullet and buy a true tilt-shift lens and adapter
examples include:
Kipon adapters for 35mm full frame lenses (search Ebay for them)