(I should note that #JeffTunnell of #Sierra/#Dynamix has since come up with #ContraptionMaker at https://store.steampowered.com/app/241240/Contraption_Maker : with its rotation physics, part generator, and countless quality-of-life improvements, it should be considered the gold standard for 2D physics educational software disguised as a game https://twitter.com/pierrelebeaupin/status/984161662231089155 )