There's a Player Guide, which explains the objective, and how to control the game. Download the Player Guide from the Download Page. See also: The Sentinel for an overview of the original gameplay and its history.
No plans for MacOS or Linux are planned. However, Zenith runs on the Wine emulator for Linux, albeit with a few problems viewing hints and energy count. Zenith uses OpenGL and OpenAL, so there is potential for re-writing for other operating systems, but this will not be considered until the game is mature.
Zenith uses a procedural algorithm to generate landscapes from a single number. Zenith uses different algorithms than the original Sentinel game, to generate a wider variety of landscapes.
Not telling! ...much. Zenith could do with a better campaign mode, where the progression more closely resembles The Sentinel. Sounds will be improved, textures will be introduced if they improve the experience, and some alternative game variations are planned.
Not in the foreseeable future.
Press F9 to view the console window, then type HELP to get a list of commands, which cover various options like controls, graphics quality, game tweaks, and some cheats. You can also put these commands into your own scripts, and into the UserPreferences.zsc file which is run when Zenith starts, and DefaultStartGame.zsc which is run at the start of every game. All scripts are held in the scripts folder, and can be edited in a simple text editor like Notepad.
The project might be resumed later in the year. In the meantime, I do not plan to release source code (see FAQ 5).