Based on the number of YouTube views, this video has made the rounds already, but it was new to me as of yesterday. The maker has created a modular marble track system. The input and output locations for the marbles are standardized at the transition points between going up and going down. Separate components are made for the the marble lift and marble run, with the lifts typically attached to the main base. In this way, one elevator system can be used to raise the marbles for several different downward runs. What a fantastic idea! It's beautifully made stuff too. Each machine measures only 10cm x 15cm at the base, so they are quite small.
[ Thanks Bob! ]