I think this is one of my own favorite projects of all time! It's 2 continuous servos connected to a lipo battery powered esp8266 that hosts a webpage with a remote control. I spent more hours than you can imagine playing with it. https://www.youtube.com/watch?v=YUY0712q7UU

One of my favorite games when I was a young child was a bottle cap race. Looking back, the realisation that anywhere I would go I could find the toy and the track could be literally anything I could get away with (even the absence of track is a track design) was very important. So much that today I work for a company that has the moto "The World is a Construction Kit".