I thought that Carl Geartrix's working TPO car was cool, and just yesterday I wrote about Mike Pianta's hopper with working suspension. Today, I was pleased to see Eurobricks user Esben Kolind's Commuter Train with working doors!
Train builders are really stepping things up, building automation and detail into rolling stock in ways that I think we could only dream about before. This build really shows the power of the PF system, and how it can be integrated into trains in interesting ways. Check out the Eurobricks post to see video of the doors in action, and a full explanation of how they work.