OpenTTD - free graphics files
OpenTTD is an open source simulation game based upon the popular Microprose game "Transport Tycoon Deluxe", written by Chris Sawyer. It attempts to mimic the original game as closely as possible while extending it with new features.
This package provides free to use graphics file. You can use them if you don't have the files from the original Transport Tycoon Deluxe game.