The Olympus Zuiko MACRO 50mm f/3.5 is one of the earliest and most famous lenses designed for the OM system. Olympus made a number of macro lenses for use with bellows, and they also had an extreme version of this lens (f/2.0 aperture). But the f/3.5, with its 1:2 magnification on 135 format was always a favorite and with good reason.
There are some great macro lenses for Micro Four Thirds, as well as easily adaptable Four Thirds ones, which also offer autofocus; although the latter is not a priority for macro work anyway. As good as these lenses are, the Zuiko 50mm f/3.5 still remains a great choice. It may be of relatively slow aperture but is very sharp even wide open. Typical of macro lenses, it presents a flat field with virtually no distortions at all. Another advantage is being a very compact lens (albeit metal => on the heavy side), again a characteristic of film-era Zuikos.
Apart from customary 1:1 macro work, since it has a 100mm FoV equivalent representation on m43, it can also be used as a portrait lens or short telephoto for general photography. Its colors and rendering, I have found to be characteristic of old Zuikos, with realistic reproduction and great contrast. Due to multicoating, it also resists flare very well, while also exhibiting very low chromatic aberrations. But it's edge to edge sharpness that sets it apart and, considering its modest cost, makes it a great option to adapt for m43.
Here follows a small gallery of photos taken with this lens, all on the OM-D E-M1, including both macro/close-up and general photography pictures: