The best ones were the long see-saw plank mounted atop a swivel post.....kinda like a kamikaze merry-go-round with a tilt-a-whirl flavor...... it’s some nasty crap that happens when one falls off....the remaining one gets a nasty ground crash in two dimensions.
Oh my goodness, I was just lurking on this thread thinking about that kind of see-saw. We had one when I was in first grade. I figured nobody would believe such a contraption existed, so I didn't mention it. As I recall no kid ever was badly injured by it, but it sure taught us to be quick, cause if that thing hit you it smarted right much. Still it was my favorite ride on the whole playground.