My son likes building blocks and likes playing with little trains that roll on wooden tracks.  These pieces allow them to be combined in a more direct manner.  They are compatible with multiple brands of building blocks and wooden train tracks as well as other projects on this site (see partial listing below).  The track and crossing plates can be used as conventional track pieces or in an elevated manner by sandwiching building blocks between two plates.  Naturally, an elevated track section requires a ramp to reach it, which is what the ramp pieces are for (the provided ramp stl files are for a plate which has been elevated by 4 standard height building blocks built on top of another track plate).  Due to size and shape constraints, the ramps are printed in separate pieces and friction fit together (although glue could be added if desired).  When oriented appropriately, all of the ramp pieces can be printed without supports.

Some compatible projects:

https://www.printables.com/model/78717-uberbloxmini

https://www.printables.com/model/117903-extended-set-of-wooden-train-track-with-50-unique-

https://www.printables.com/model/97448-simple-track-cars