Algodoo

It`s a monorail track.
It runs automatically by itself, you just need to change the junctions and stuff.

Left and Right Arrow Keys -> Switch the purple tracks.

Up and Down Arrow Keys -> Change the yellow track.

Thanks to RaRaMalum for inventing the Raunit, which in this case is used to stabilise the carriage. It still works without it though.

This is my first submission.