- spring actuated forklift loaders
- boat hulls that actually float in water
- airplane/helicopter rotors (incompatible with technics because they predate it)
Not to mention all the doors, windows, trees, wheel axles and pulleys that can really only do one thing.There was a period in the late 90s/early aughts when Lego really went adrift with the single function pieces. I got my kids a Lego airplane set from that era that consists basically of plane parts. No matter what you do with those pieces they look like they're parts of an airplane. It's pretty sad.
Fortunately, Lego corrected course. They still make specialized pieces, particularly the minifigs. When you're working at that scale, nearly all the minifig tools are going to consist of a single piece. But most of the sets now consist of largely of pieces that are flexible enough to be assembled into anything. Sets from the Creator line come with a booklet to assemble whatever is on the box (eg. a robot or a dinosaur), but none of the pieces are so specialized that they can only be used for one thing.