In a post apocalyptic society, a shortage of manpower and equipment would necessitate finding alternatives. Zombies are plentiful, simple, and predictable. As a result there are plenty of things you could do with a properly restrained and contained zombie.
Electrical power generation (zombie treadmill/hamster wheel) https://en.wikipedia.org/wiki/Treadwheel
Electrical power generation 2: A carefully contained shocker zombie would allow for free power. All it would require is a grounding system inside their containment unit to draw off the charge they generate. The damn things are walking tesla coils after all, so copper plates or something would work.
Grinding various substances like grain into flour. https://en.wikipedia.org/wiki/Horse_mill
Mechanical Power: Cranes, elevators, cargo lifts, etc powered by a treadwheel system with belts and gears.
Acid Synthesis: Restrain a spitter or corrosive zombie above a tank of water, and give it a target. Acid emissions will mix with water to dilute into a more containable form, for use as feedstock for various purposes.
Zombie Oxen: Yoke a bunch of zombies with blinders to a wagon or sled and use them to pull it. Use an animal or something at the front as bait to make them move forwards.
I’m sure there are plenty of other applications.