Linux (requires SDL and SDL_mixer. If lagging, start with "simutrans -nomidi"). Simutrans runs on Windows, Linux, BeOS, MAC OS X, and can be compiled on many more systems (it just requires either SDL or Allegro). To be able to play, You need one executable compatible with your operating system and at least one of the paksets. For beginner, the pak64 is recommended, since this should work always and is easier than the other paksets.