AutoRouted Rail uses turtles, entity sensors and a central coordination server accessed over websocket to automatically route minecarts to player-selected destinations. While some other implementations were based on computer minecarts, ARR uses passive tracks (using normal powered rails) and minecarts, but with computer-controlled switches using on-demand greedy routing, as well as smart stations to automatically dispense carts. While originally intended to run Chorus City's hypothetical public transit infrastructure, lack of a compelling usecase for public transit infrastructure, minor issues with station physical implementation and the lack of a clear way to generalize the routing sensibly to busy systems without highly redundant paths meant it has only ever been deployed for testing.
A screaming bird of truth.