Newtons Gravity puzzle
Looking through Instructables, I happened across this (https://www.instructables.com/id/How-to-Make-a-Newtons-Gravity-Puzzle/ by tomatoskins), and thought "Gee, that would be doable in plastic." Ten minutes in TinkerCAD, and here it is.
Object - Remove the center piece without tools. You must keep the outer ring flat on a tabletop.
It should probably be called Bernoulli's Principle Puzzle (nudge, nudge, wink, wink). Past that, I'll let you figure out how to solve it. Or, you could visit the inspiring original Instructables. The solution is at the bottom of the article.
The concentric version prints quickly.