You can find both versions of the game at www.openttd.org. The OS/2 port is maintained by Owen Rudge, please direct any OS/2-specific issues to orudge[@]openttd[.]org.
OpenTTD is a clone of the Microprose game "Transport Tycoon Deluxe", a popular game originally written by Chris Sawyer. It attempts to mimic the original game as closely as possible while extending it with new features.
OpenTTD is licensed under the GNU General Public License version 2.0. For more information, see the file 'COPYING' included with every release and source download of the game.
Please note that you need the original Transport Tycoon data files in order to be able to play OpenTTD. See the web site for more information.