Open Transport Tycoon is an open source "clone" of Transport Tycoon, the best Railroad Tycoon like game ever released
. It's really great, the original binaries of TTDeluxe have been disassembled and converted to C, so it's as close to the original as possible (It needs the original TTDeluxe data files to run, like ScummVM).
There are now Versions for Windows, Linux and recently AmigaOS and MorphOS
Heres a screenshot of it running on MorphOS: http://www.christianrosentreter.com/cache/ottd2.png