there are also many nice prime lenses, each with their own advantanges and disadvantages
there is also an enormous range of manual focus lenses which can be used, including some in Micro Four Thirds mount
if almost zero distortion is important to you, then the best option is the superb, but heavy and expensive Olympus ZD 7-14mm f/4 lens although this is not CDAF compatible and thus AF will be very slow unless you have a phase detect camera
at 25mm is not wide angle but a “standard” 50mm field of view lens and thus a nice compliment to the Olympus 17mm lens or Panasonic 15mm lens
compact pancake lenses
these are all relatively old lenses with slow and noisy AF, but they are very handy for reducing the size of your camera to allow it to fit in a jacket pocket
the most sought after of these is the very sharp, wide aperture, Panasonic Lumix 20mm f/1.7 pancake lens although bokeh can be a bit distracting, it does have a bit of purple fringing, and at ISO 1600 and higher it may cause sensor banding noise
the Olympus m.ZD 17mm f/2.8 pancake lens has mixed reviews and its f/2.8 aperture makes it less versatile than the Panasonic 20mm, and thus may not give much advantage over a compact 3x zoom lens which are f/3.5 at that aperture.