Hornbeam (Hainbuche) appears very similar to beech (Rotbuche), though they're not particularly closely related.
Hornbeam has pointy, serrated leaf edges, whereas the leaves of beech are smoother and more wavy in shape. Beech has seed pods, whereas hornbeam has these sort of winged seed bundles. Beech foliage (Rotbuche in particular) will take on a reddish shade in the autumn, from which it derives its name.
Hornbeam is known for its very hard wood, which is often used for tools and mechanisms. Seems like hornbeams can develop some real cool, gnarly looking trunks, which may be related to frequent coppicing back in the day.