Simutrans plans the move to Steam. The game will be available for free on the distribution platform. This might help new players to get to know the game, and those who already play the game and also use Steam an easier way to keep Simutrans up to date. If you do not use Steam, don’t worry, all other ways of distribution that are currently used, for example, source code, binaries, Windows-installer, and inclusion in many Linux installers will still be available.
Steam is a large, commercial game distribution platform, that means they sell games online, provide downloads that are started from within Steam. Steam is avaible for Windows, Mac-OS, and Linux (SteamOS). Greenlight is Steam’s procedure to get games to the platform that do not have a large publisher behind them. I.e, indie-developers or open source. Steam users can vote for games to pass Greenlight, and if you have a Steam account, we should be very happy if you did so. You can vote for Simutrans on its Greenlight page.