A typical display of my LEGO spintoys at last weekend's hobby show in Denver...
https://youtu.be/uCaRtahadQcFor safety and other reasons, I usually have visitors point to spintoys for me to demo. The optically active color-mixing, B&W stroboscopic, and blacklight tops entering at 2:02 generally get the most oohs and ahhs.
Other mechanical LEGO gizmos on display include a train-driven orrery (here missing its central star), a self-folding pneumatic cube, and several remote control vehicles. Of these, the cube and the fully functional RC excavator are perennial crowd-pleasers. The always-moving cube and orrery serve as eye-catchers.
Many of the items here appear in more detail in other videos on this channel.