I loved "The Incredible Machine" as a kid! This definitely reminded me of that. I wish I could move objects after placing them without deleting my entire build— not being able to makes this a lot harder! Also like others have mentioned, the physics aren't deterministic, so sometimes you can have a build that succeeds sometimes and fails other times. That would be essential to fix up for a full version!
Overall, a splendid little physics puzzler 😀